Actually people needs to understand that the facts presented in the oldest Sanskrit scriptures written atleast 2800 years ago doesn't paint the picture of events of Mahabharata completely similar to that of latter Sanskrit retellings,regional folklores, novels and entertainment media. Here's the episode of Karna's death by Arjuna present by Mahabharata CE which is certified as the most authentic Sanskrit version of Mahabharata by orientalists/historians :-
Karna Parva, Section-67 Shloka No.8 -Shloka No. 26
8 तं समीक्ष्य ततः कर्णॊ बरह्मास्त्रेण धनंजयम
अभ्यवर्षत पुनर यत्नम अकरॊद रथसर्जने
तद अस्त्रम अस्त्रेणावार्य परजहारास्य पाण्डवः
9 ततॊ ऽनयद अस्त्रं कौन्तेयॊ दयितं जातवेदसः
मुमॊच कर्णम उद्दिश्य तत परजज्वाल वै भृशम
10 वारुणेन ततः कर्णः शमयाम आस पावकम
जीमूतैश च दिशः सर्वाश चक्रे तिमिरदुर्दिनाः
11 पाण्डवेयस तव असंभ्रान्तॊ वायव्यास्त्रेण वीर्यवान
अपॊवाह तदाभ्राणि राधेयस्य परपश्यतः
12 तं हस्तिकक्ष्या परवरं च बाणैः; सुवर्णमुक्ता मणिवज्र मृष्टम
कालप्रयत्नॊत्तम शिल्पियत्नैः; कृतं सुरूपं वितमस्कम उच्चैः
13 ऊर्जः करं तव सैन्यस्य नित्यम; अमित्रवित्रासनम ईड्य रूपम
विख्यातम आदित्यसमस्य लॊके; तविषा समं पावकभानु चन्द्रैः
14 ततः कषुरेणाधिरथेः किरीटी; सुवर्णपुङ्खेन शितेन यत्तः
शरिया जवलन्तं धवजम उन्ममाथ; महारथस्याधिरथेर महात्मा
15 यशश च धर्मश च जयश च मारिष; परियाणि सर्वाणि च तेन केतुना
तदा कुरूणां हृदयानि चापतन; बभूव हाहेति च निस्वनॊ महान
16 अथ तवरन कर्णवधाय पाण्डवॊ; महेन्द्रवज्रानल दण्डसंनिभम
आदत्त पार्थॊ ऽञजलिकं निषङ्गात; सहस्ररश्मेर इव रश्मिम उत्तमम
17 मर्मच छिदं शॊणितमांसदिग्धं; वैश्वानरार्क परतिमं महार्हम
नराश्वनागासु हरं तर्यरत्निं; षड वाजम अज्ञॊ गतिम उग्रवेगम
18 सहस्रनेत्राशनि तुल्यतेजसं; समानक्रव्यादम इवातिदुःसहम
पिनाक नारायण चक्रसंनिभं; भयंकरं पराणभृतां विनाशनम
19 युक्त्वा महास्त्रेण परेण मन्त्रविद; विकृष्य गाण्डीवम उवाच सस्वनम
अयं महास्त्रॊ ऽपरतिमॊ धृतः शरः; शरीरभिच चासु हरश च दुर्हृदः
20 तपॊ ऽसति तप्तं गुरवश च तॊषिता; मया यद इष्टं सुहृदां तथा शरुतम
अनेन सत्येन निहन्त्व अयं शरः; सुदंशितः कर्णम अरिं ममाजितह
21 इत्य ऊच्चिवांस तं सा मुमॊच बाणं; धनंजयः कर्णवधाय घॊरम
कृत्याम अथर्वाङ्गिरसीम इवॊग्रां; दीप्ताम असह्यां युधि मृत्युनापि
22 बरुवन किरीटी तम अतिप्रहृष्टॊ; अयं शरॊ मे विजयावहॊ ऽसतु
जिघांसुर अर्केन्दुसम परभावः; कर्णं समाप्तिं नयतां यमाय
23 तेनेषु वर्येण किरीटमाली; परहृष्टरूपॊ विजयावहेन
जिघांसुर अर्केन्दुर समप्रभेण; चक्रे विषक्तं रिपुम आततायी
24 तद उद्यतादित्य समानवर्चसं; शरन नभॊ मध्यग भास्करॊपमम
वराङ्गम उर्व्याम अपतच चमूपतेर; दिवाकरॊ ऽसताद इव रक्तमण्डलः
25 तद अस्य देही सततं सुखॊदितं; सवरूपम अत्यर्थम उदारकर्मणः
परेण कृच्छ्रेण शरीरम अत्यजद; गृहं महर्द्धीव ससङ्गम ईश्वरः
26 शरैर विभुग्नं वयसु तद विवर्मणः; पपात कर्णस्य शरीरम उच्छ्रितम
सरवद वरणं गैरिकतॊय विस्रवं; गिरेर यथा वज्रहतं शिरस तथा
Translation :- “On seeing this, Karna again invoked brahmastra against Dhananjaya. He showered down arrows
and tried to extricate his chariot. Pandava countered those weapons with his own weapons. Kounteya then released another weapon, beloved of the fire god, towards Karna. It blazed fiercely. Karna pacified the fire through a varuna weapon. He covered all the directions with clouds and it was as dark as a rainy day.
Pandaveya was not frightened. While Radheya looked on, the valiant one used the
vayavya weapon and dispelled all the clouds. The supreme one’s standard had the marks of an elephant’s housing. It was decorated with gold, pearls, jewels and diamonds. It had been crafted by excellent artisans over a long period of time. It was expensive and beautiful in form.
It always inspired your soldiers and terrified and frightened the enemy. It was renowned in the world and blazed like the sun and the moon. Kiriti used a razor-sharp arrow that was gold-tufted and pointed. With that, he brought down the handsome and blazing standard of the great-souled maharatha, Adhiratha’s son. O venerable one! When that standard was uprooted, fame, dharma, victory and
everything that was dear to the hearts of the Kurus also fell down. Great sounds of lamentation arose. ‘ “To ensure Karna’s death, Pandava took out an anjalika arrow. It was like the great Indra’s vajra, or like a rod that was made out of fire. It blazed in its rays, like the one with one thousand rays. 800 It was capable of penetrating the inner organs and smearing itself with blood and flesh.
It was extremely expensive and was like the fire and the sun. It could destroy men, horses and elephants and was three cubits long, with six tufts. 801 It travelled straight and possessed a great force. In its energy, it was like the vajra of the one with one thousand eyes. It was as difficult to withstand as predatory beasts. It was like the pinaka and Narayana’s chakra. It was fearful and destructive of living beings.
He invoked mantras and affixed that supreme and great weapon to Gandiva. He loudly said, ‘I am grasping this great weapon, which is in the form of an arrow. It is extremely difficult to withstand and is capable of destroying the body. If I have tormented myself through austerities and have satisfied my seniors, if I have listened to what my well-wishers have told me, through that truth, let this arrow slay my armoured enemy, Karna, and bring me victory.’ Having said this, for the sake of Karna’s death, Dhananjaya released that terrible arrow. It was as fierce as rites performed by Atharvan and Angiras. It blazed and was impossible to be endured in a battle, even by Death itself. Kiriti cheerfully said, ‘Let this arrow bring me victory.’ Wishing to slay Karna, bring about his end and convey him to Yama, he released the arrow, which was as radiant as the sun and the moon. Cheerfully, so that he could be conveyed towards victory, the one with the diadem and the garland shot the arrow. It was as radiant as the sun and the moon. He harboured feelings of enmity and wished to slay his enemy. That weapon, blazing like the sun, was shot. Like the sun, it lit up the earth with its radiance. The head of the commander of the army was severed. Like the sun, with a red disc, it seemed to set. The body of the one who performed generous deeds was always reared in happiness.
Like a person who is reluctant to leave a house filled with great riches, the head parted from the body with great difficulty. Without the armour, the body was mangled by arrows and lost its life. Karna’s body was severed and fell down.
So according to original Mahabharata The last activity done by Karna was to cover the cover the who battlefield using his arrows after shooting Varunastra and furthermore the previous military record of Arjuna also says that Karna wasn't that worthy opponent for Arjuna.