He does say that he is sufficient:
Sarva-dharman parityajya mam ekam saranam vraja: "Give up all other duties and surrender unto Me."
If he says anywhere that he is necessary - that would make Bhagavad Gita a sectarian document.
This actually depends on the commentator or the one who is reading it. This link shows that Sri Adi Shankaracharya means the Real Self by 'Me' here, whereas some others mean Narayana. And this link shows it means Lord Krishna: https://asitis.com/18/66.html
It is very cllear that Vishnu, Shiva, Shakti and Surya are just the altrnative forms of the Supreme Godhead according to Mahabharat and Gita , because:
In Gita, Arjuna refers to Sri Krishna as Vishnu so many times and so equality of Vishnu and Krishna is well established.
We get Adityas in plural number while Surya is used always in the ekavachana meaning He is One. In the Vishnusahasranama, which is a part of the Mahabharata as is the Gita, the name ‘Surya’ has been mentioned. This means the equlity of Surya and Krishna is established in the Mahabharata.
Different names of Shiva like Swambhu, Sambhu and also also Shiva are mentioned in the Vishnusahasranama. This establishes the equality of Vishnu and Shiva. By the way, the name “Rudra” is not mentioned even in the Shivasahasranama in Mahabharata, meaning that the eleven Rudra were considered a devata and not God.
Sri Krishna asks Arjuna to pray to Mother Durga before the Kurukshetra war starts (Bhishmaparva, 23/2). In Arjuna’s parayer, Durga has been mentioned as “Janani” (Universal Mother) and “Swadha”(a sacred mantra). In Gita, Sri Krishna says that He Himself is the Universal Mother and Swadha. So the unity of Durga and Krishna is established in Mahabharata and so Gita.
At the same time, the Gita accepts the four words of the Absolute forms : Brahman(chapter 8, sloka 13), Atma(chapter 10, sloka 20), Ishwar(chaper 18, sloka 61), and Bhagavan(He is always referred to as Sri Bhagavan in Gita). So Gita is a Scripture of Synthesis: (i) Of the forms of Yogas (Karmayoga(chapter 3,sloka 19) jnanayoga (chapter12,sloka 3&4) Rajayoga (chapter 5, sloka 27 & 28) and Bhaktiyoga(chapter 11,sloka 54), and (ii) Of all the names of the Absolute forms and (iii) Of all the names of the Hindu Godheads.
Quite naturally, it has been the treasure of all the sects belonging to the Sanatana Dharma.
Sri Ramakrishna has explained the equality of God the Self beautifully. He says one's Ishtadevata is His or Her real Self.(Ref: Sriramkrishnake jerup dekhiyachhi, udbodhan karyalaya).According to Sri Sitaramdas Omkarnath,a great saint of the modern time, who actually belonged to the Ramanuja-Ramanandi sect, says that all mantras ultimately merges in OM and its the Para Pranava Who is the Real Self.(Reference: Sudhar Dhara,Sri Sri Sitaramdas Omkarnath).He has written the Pranava Prema Pijusha Vashya of Gita which has been published by the Mahamilan Math.
To conclude, this "Me" of Gita is the God or the Ultimate for any spiritual seeker.
Yes, Krishna does discuss such exclusivity. Here is what he says in chapter 9 verse 25 of the Bhagavad Gita:
yānti dēvavratā dēvān pitṛnyānti pitṛvratāḥ |
bhūtāni yānti bhūtējyā yānti madyājinō.pi mām৷৷
Those who worship the demigods will take birth among the demigods; those who worship the ancestors go to the ancestors; those who worship ghosts and spirits will take birth among such beings; and those who worship Me will live with Me.
Here is what Adi Shankaracharya says about what "those who worship Me" means:
yānti gacchanti dēvavratāḥdēvēṣu vrataṅ niyamō bhaktiśca yēṣāṅ tē dēvavratāḥ dēvān yānti |
pitṛn agniṣvāttādīn yānti pitṛvratāḥ śrāddhādikriyāparāḥ pitṛbhaktāḥ |
bhūtānivināyakamātṛgaṇacaturbhaginyādīni yānti bhūtējyāḥ bhūtānāṅ pūjakāḥ |
yānti madyājinaḥ madyajanaśīlāḥ vaiṣṇavāḥ māmēva yānti |
Deva-vratah, votaries of the gods, those whose religious observances [Making offerings and presents, circumambulation, bowing down, etc.] and devotion are directed to the gods; yanti, reach, go to; devan, the gods. Pitr-vratah, the votaries of the manes, those who are occupied with such rites as obsequies etc., who are devoted to the manes; go pitrn, to the manes such as Agnisvatta and others. Bhutejyah, the Beings such as Vinayaka, the group of Sixteen (divine) Mothers, the Four Sisters, and others. And madyajinah, those who worship Me, those who are given to worshipping Me, the devotees of Visnu; reach mam, Me alone.
And here is what Ramanuja says about this verse:
The term ‘Vrata’ in the text denotes will, intention or motive. Those who intend to worship gods, like Indra and others with the resolution, ‘Let us worship Indra and other gods by ceremonies like the new moon and full moon sacrifices’ — such worshippers go to Indra and other gods. Those who intend worshipping manes, resolving ‘Let us worship the manes through sacrifices,’ — such worshippers go to the manes or others resolving — ‘Let us worship the Yaksas, Raksasas,’ Pisacas and other evil spirits’ — they go to them. But those who, with the same rites of worship, worship Me with the intention, ‘Let us worship Lord Vasudeva, the Supreme Self, whose body is constituted of gods, the manes and the evil spirits’ — they are My worshippers and they reach Me only. Those who intend worshipping gods etc., attain gods etc. After sharing limited enjoyment with them, they are destroyed with them when the time comes for their destruction. But My worshippers attain Me, who has no beginning or end, who is omniscient, whose will is unfailingly effective, who is a great ocean of innumerable auspicious attributes of unlimited excellence and whose bliss too is of limitless excellence. They do not return to Samsara. Such is the meaning. Sri Krsna continues to say, ‘There is also another distinguishing characteristic of My worshippers.’
But none of this makes the Bhagavad Gita a sectarian document; it is the nectar of the Upanishads. As the Gita Dhyana Sloka says, "The Upanishads are the cows milked by Gopāla, the son of Nanda, and Arjuna is the calf. Wise and pure men drink the milk, the supreme, immortal nectar of the Gita."
This depends upon sect & one's own interpretations. There are some yogic commentaries like of Yogānanada's etc which interpret BG for yogis whereas some commentaries interpret the same text for 'devotees'. In fact, christian commentaries are also now available in the market now. So, it's wrong to cover BG in single blanket.
And Even that verse of 'Sharnagati' doesn't make it globally sectarian. For example, Kashmiri Shaiva enlightened mystic Abhinavgupta at the end of BG referring the verse you detailed, comments
Whatever action might be performed by a Yogin - who has freed his mind dominated by the three gunas, which are the nature of knowledge, ,confusion & inertia, and who has attained Vishnu, who is beyond thought, through the beauty of realization of his own self - the action is performed effortlessly because he is engaged only in such activities of the sense organs, which arise in him on their own. To such a Yogin Siva is everything.
But one should also note that the mystic Abhinavgupta neither wrote commentary to maintain vedAntic conformity (although he was initiated in vedAnta as well) nor to impose Shaivite agenda but rather he wrote as a personal gift for his VaishNava friend Bhatta NarayaNa on the later's request. But due to its unique esoteric/tantrik eloquence the commentary became famous.
Arjuna was addressed with purusa rishabha in 2.15
यं हि न व्यथयन्त्येते पुरुषं पुरुषर्षभ। समदुःखसुखं धीरं सोऽमृतत्वाय कल्पते
Krishna addressed himself as purusa uttama in 15.18
यस्मात्क्षरमतीतोऽहमक्षरादपि चोत्तमः। अतोऽस्मि लोके वेदे च प्रथितः पुरुषोत्तमः
since rishaba means best & uttama also is superlative meaning the best. There is no question of granting moksha as they are equal.
We know purusa sukta is of Vishnu.
And Arjuna wanted to know about purusa in 13.1
प्रकृतिं पुरुषं चैव क्षेत्रं क्षेत्रज्ञमेव च। एतद्वेदितुमिच्छामि ज्ञानं ज्ञेयं च केशव
There is no question a deity granting moksha as per this analysis. All are liberated already.
Hope it helps!!
There are three ways : Karma, Gyana and the Bhakti. All of them grant liberation (moksha).
Nevertheless, Krishna explains in B.Gita liberation (moksha) as the worst position in devotion. The desire for liberation (moksha) is an end to devotional progress. The soul has been considered as part and parcel of God (super soul), which has been called as eternal servant of the Almighty.
That's why Krishna has been very humorously telling arjuna in B.Gita, " sarva dharman parityajya, maam ekam sharnam braj; aham tvaam sarv paapebheyo moxiyami maasuchah."
He says, "Maam" mine and emphasizes with "ekam" only. Surrendering unto Him alone could get arjuna liberation (moksha) undoubtedly from the sins (here "maasuchah" means, Krishna being humorously telling not to think about liberation by mitigating the sins). The sins which Arjuna was worried about in the middle of the battlefield. Arjuna was thinking on the material platform, however, Krishna finally convinced him that atleast liberation (moksha) would be his destination if he surrendered unto Him, in the battlefield fighting for the justice.
The moksha or liberation is an endless end to the spiritual journey to God. The moksha brings end to the devotional life. The moksha is a spiritual lethargy. It has been confirmed as the worst enemy ("kaitabh") of the devotees.