Is it true that Sugreeva's elder brother Vaali was stronger than Lord Rama himself?
How is it possible for a vanara to be more powerful than a God?
No, Vali was not stronger than Lord Rama. Same question has been asked by Sugriva in Kishkindha Kanda, Sarga 11.
इमे च विपुलास्सालास्सप्त शाखावलम्बिनः।
यत्रैकं घटते वाली निष्पत्रयितुमोजसा4.11.67।।
'Look at these seven sturdy Sala trees with branches of one overlapping the other. Vali was able to remove all the leaves of one Sala tree with just one arrow.
एतदस्यासमं वीर्यं मया राम प्रकीर्तितम्।
कथं तं वालिनं हन्तुं समरे शक्ष्यसे नृप4.11.68।।
'O Rama Vali's strength and fame related by me is unequalled. O king how is it possible for you to kill him in a combat?'
Then Lord Lakshamana had asked Sugriva that what should be done by Sri Rama to prove his strength.
तथा ब्रुवाणं सुग्रीवं प्रहसन् लक्ष्मणोऽब्रवीत्।
कस्मिन्कर्मणि निर्वृत्ते श्रद्दध्या वालिनो वधम्4.11.69।।
Smiling, Lakshmana asked Sugriva, 'By what action will you trust?. By the fulfilment of which task (by Rama) will you have faith?'
Then Sugriva had given two tasks to Sri Rama (politely) as: To split through sala tree and moving the skeleton of the demon Dundubhi at the distance of 200 bows.
तमुवाचाथ सुग्रीवस्सप्त सालानिमान्पुरा।
एवमेकैकशो वाली विव्याथाथ स चासकृत्। 4.11.70।।
Then Sugriva told Lakshmana that earlier Vali had split through these seven Sala trees one after the other, several times.
रामोऽपिदारयेदेषां बाणेनैकेन च द्रुमम्।
वालिनं निहतं मन्ये दृष्ट्वा रामस्य विक्रमम्4.11.71।।
'If I see Rama splitting these trees with one arrow, I will believe he can kill Vali with his prowess.
हतस्य महिषस्यास्थि पादेनैकेन लक्ष्मण।
उद्यम्याथ प्रक्षिपेच्चेत्तरसा द्वे धनुश्शते4.11.72।।
'O Lakshmana and if Rama can also lift the dead buffalo's (Dundubhi's) skeleton and hurl it to a distance of two hundred bows with one of his feet.
Then Sri Rama has completed these tasks without any difficulty.
तस्य तद्वचनं श्रुत्वा सुग्रीवस्य महात्मनः।
स्मितपूर्वमथो रामः प्रत्युवाच हरिं प्रभुः4.11.82।।
Having heard the great Sugriva, Rama replied with a gentle smile:
यदि न प्रत्ययोऽस्मासु विक्रमे तव वानर।
प्रत्ययं समरे श्लाघ्यमहमुत्पादयामि ते4.11.83।।
'If you have no confidence in my strength in fight, O monkey, I will create it in you so much so that you will admire it.'
एवमुक्त्वा तु सुग्रीवं सान्त्वं लक्ष्मणपूर्वजः।
राघवो दुन्दुभेः कायं पादाङ्गुष्ठेन लीलया4.11.84।।
तोलयित्वा महाबाहुश्चिक्षेप दशयोजनम्।
असुरस्य तनुं शुष्कं पादाङ्गुष्ठेन वीर्यवान्4.11.85।।
Rama,the mighty elder brother of Lakshmana, having said so to Sugriva in a pleasing manner, lifted the dried body of Dundubhi easily with his toe, shook it and flung it with ease to a distance of ten yojanas.
Sri Rama's piercing Sala tress is described in Sarga 12.
स गृहीत्वा धनुर्घोरं शरमेकं च मानदः।
सालमुद्दिश्य चिक्षेप ज्यास्वनैः पूरयन्दिशः। 4.12.2।।
Rama, subduer of the enemy's pride, strung his terrific bow, produced the twang that filled all directions, and discharged a single arrow aimed at the sala tree.
स विसृष्टो बलवता बाणस्स्वर्णपरिष्कृतः।
भित्त्वा सालान् गिरिप्रस्थं सप्त भूमिं विवेश ह4.12.3।।
Released with great force, Rama's arrow embellished with gold pierced through the seven sala trees and splitting the mountain terrain entered the earth.
प्रविष्टश्च मुहूर्तेन धरां भित्त्वा महाजवः।
निष्पत्य च पुनस्तूर्णं स्वतूणीं प्रविवेश ह4.12.4।।
In a moment the arrow emerged from the earth which it pierced and reentered the quiver with great speed.
Then Sugriva was struck by wonder and accepted the strength of Sri Rama.
तान्दृष्ट्वा सप्त निर्भिन्नान्सालान्वानरपुङ्गवः।
रामस्य शरवेगेन विस्मयं परमं गतः4.12.5।।
The chief of the monkeys was struck with wonder seeing Rama's arrow piercing through the seven sala trees so swiftly.
स मूर्ध्ना न्यपतदभ्मौ प्रलम्बीकृतभूषणः।
सुग्रीवः परमप्रीतो राघवाय कृताञ्जलिः4.12.6।।
Sugriva was immensely happy and offered obeisance to Rama with folded hands and bowed down and prostrated while his ornaments touched the ground.
इदं चोवाच धर्मज्ञं कर्मणा तेन हर्षितः।
रामं सर्वास्त्रविदुषां श्रेष्ठं शूरमवस्थितम्4.12.7।।
Sugriva who stood by, elated to watch the deed of Rama, best among the valiant, proficient in the use of arms of all kinds and knower of dharma, said:
सेन्द्रानपि सुरान्सर्वांस्त्वं बाणैः पुरुषर्षभ।
समर्थस्समरे हन्तुं किं पुन र्वालिनं प्रभो 4.12.8।।
'O bull among men, O lord, you are capable of killing with your arrows even the gods including Indra in the battle, what to speak of Vali.
येन सप्तमहासाला गिरिर्भूमिश्च दारिताः।
बाणेनैकेन काकुत्स्थ स्थाता ते को रणाग्रतः4.12.9।।
'O Rama who can in a battle confront you, capable of splitting seven huge sala trees, the mountain and the earth with a single arrow?
अद्य मे विगतश्शोकः प्रीतिरद्य परा मम।
सुहृदं त्वां समासाद्य महेन्द्रवरुणोपमम्4.12.10।।
'Having found a friend in you comparable to Indra and Varuna, my grief is gone and I am so happy now.
तमद्यैव प्रियार्थं मे वैरिणं भ्रातृरूपिणम्।
वालिनं जहि काकुत्स्थ मया बद्धोऽयमञ्जलिः4.12.11।।
'O Rama, for my pleasure kill Vali who is, to me, an enemy in the guise of a brother. I fold my hands to you.
Possibly true. No one can give a definite answer to this question because Rāma never engaged himself in a one-on-one fight with Vāli to solve this mystery once and for all.
There's an interesting verse, however, from Vālmīki Rāmāyaṇa when Sugrīva is narrating the Dundubhi-Vāli fight to Rāma.
परस्परं घ्नतो स्तत्र वानरासुरयोस्तदा। आसीदसुरो युद्धे शक्रसूनुर्व्यवर्धत 4.11.44 ।।
तदा then, तत्र there, वानरासुरयोः of monkey and demon, परस्परम् one to one, घ्नतोः pouncing on the other, युद्धे in fight, असुरः demon, हीनः reduced, आसीद become, शक्रसूनुः son of Indra, व्यवर्धत grew (in strength and spirit).
Then as the monkey and demon fought pouncing on each other, the prowess of Dundubhi got diminished and that of Vali, the son of Indra, increased.
Now if Sugrīva's account is true, a person who engages in a direct battle with Vāli will slowly lose their strength and Vāli becomes more and more devastating.
For comparison, in a typical heavy weight boxing match, at the end of 12 rounds, you will find both boxers heavily sweating and totally drained off of their energies.
But Vāli is unusual. His strength grew as the fight with Dundubhi progressed. So either he had remarkable stamina or he's got some super-powers.
In Uttara-kāṇḍa of Rāmāyaṇa, we see just how powerful Vāli really is:
After catching the ruler of the rakshasas who had wanted to catch him, Vali squeezed him in his armpit, and as he was hanging there, Vali jumped quickly into the sky. Although Ravana repeatedly pinched and gashed Vali with his nails, Vali carried him away, as the wind does a cloud. While Ravana was being carried away, his ministers howled and rushed upon Vali to free Ravana. While being chased by them across the sky, Vali looked like the sun being followed by masses of clouds. Unable to approach Vali, those stalwart rakshasas were exhausted by the speed of Vali arms and legs. Even great mountains retreated from Vali's pathway as he proceeded, what to speak of creatures of flesh and blood who desire to live.
Vāli is wearing the golden chest-pendent given by his father Indra, wearing which depletes half of the opponent's strength. Hence, the strength of Dundubhi is depleted now. Vāli does not wear the same chest pendent when fighting with Sugreeva when killed by Rama. For this it is said, Vāli wanted to punish Sugreeva that which is befitting to an errant younger brother, but Vāli never considered Sugreeva as a real threat or an enemy to the core.
Further, instead of engaging in a face-to-face combat, Rāma shoots and kills Vāli from behind a tree.
I find it highly unusual, the way Rāma defends his actions by calling Vāli an animal, that he was actually hunting him and there was no need for a fair fight:
प्रधावितान्वा वित्रस्तान्विस्रब्धांश्चापि निष्ठितान् 4.18.39 ।। प्रमत्तानप्रमत्तान्वा नरा मांसार्थिनो भृशम्। विध्यन्ति विमुखांश्चापि न च दोषोऽत्र विद्यते 4.18.40 ।।
मांसार्थिनः seeking flesh for food, नराः men, प्रधावितान् वा or running ones, वित्रस्तान् alarmed ones, विस्रब्धान् unalarmed, निष्ठितान् stable ones, प्रमत्तान् those that are not alert, अप्रमत्तान्वा even alert ones also, विमुखांश्च those which turn away, विध्यन्ति kill, अत्र here, दोषः blemish, न विद्यते not known.
People seeking animal flesh for food kill animals alarmed or unalarmed, animals that run away or animals that stand still. They kill animals whether they are alert or not and no blemish is attached.
Well if Sugrīva and Vāli are both "animals", why should Rāma kill one arrogant animal and install another mentally sound animal in its place on the throne? Do we have any references from scripture, where, for example, a 'bad' lion is killed by humans to install a 'good' lion as the king of the jungle? I doubt.
Also, why should Hanumān draft a friendship contract between Rāma and Sugrīva if both Sugrīva and Hanumān are "animals" according to Rāma?
'Whether you face this way or that, you are an animal, as you alone said, besides being an enemy of my friend...' For this Griffith says - I cannot understand how Vālmīki could put such an excuse as this into Rāma's mouth. Rāma with all solemn ceremony, has made a league of alliance with Vāli's younger brother whom he regards as a dear friend and almost as an equal, and now he winds up his reasons for killing Vāli by coolly saying: 'Besides you are only a monkey, you know, after all, and as such I have every right to kill you how, when, and where I like.'
Clearly, the above inconsistencies can only point to some interpolations in the Vālmīki Rāmāyaṇa.
In my opinion, if Rāma was simply punishing Vāli for being an adhārmic king, there is absolutely no reason to hide the fact that Vāli was more powerful than Rāma, by way of any interpolations.
Vāli simply needed to be eliminated one way or the other - either in a straight fight or by ambush.