Without Krishna Arjuna and the Pandavas would never have won the Mahabharata war. This was confirmed by Krishna himself.
The Pandavas were distressed and immersed in thought. On seeing this, Krishna spoke these words, in a voice that rumbled like clouds and drums. ‘All of them were swift in the use of weapons and were maharathas. In a fair fight, even if we fought bravely, we were incapable of defeating them in the battle. That is the reason I thought of means to slay those lords of men. Otherwise, the Pandaveyas would never have obtained victory.
Mahabharat Gadda Yuddha Parva Chapter 60 By Bori Ce
Fact is clear from numerous events that Kuru warriors would have killed Arjuna if not for Krishna on his side. Most important thing is that he would get the knowledge of Bhagwad Gita from Krishna to win the war
- Bhishma proved too difficult to be beaten by the Pandavas and could be brought down only when Shikhandi stood before him. It was Krishna who planned that the best way to defeat him is to ask him else killing Bhishma would be impossible.
- If not for Krishna Bhagadatta would have killed Arjuna twice on 12th day. His infalliable Vaishnavastra would have killed Arjuna had Krishna not stopped it. And his elephant Supratika would have trampled him had Krishna not skillfully guided the chariot.
- Without Krishna Arjuna would not have been able to complete his pledge of killing Jyadratha. It was Krishna who suggested Arjuna to obtain a boon from Shiva before 14th day as he was not supposed to fight in the war.
- Shrutayudh with his infalliable mace would have quite easily killed Partha on 14th day if not for Krishna present there.
- Would have been killed had Krishna not informed him of Jyadratha,’ s boon by his father that The person who fights with Jyadratha in an encounter and brings his head down on the ground his head will shatter into a hundred fragments.
- Karna with his infalliable Vasavi shakti could have killed Arjuna but it was Krishna who used his illusions to make Karna forget from using Vasavi shakti and send Ghatotkacha against Karna on 14th night so that the spear be wasted.
- Drona was unstoppable on 15th day after Duryodhana,’ s taunts of him fighting mildly against the Pandavas. All the Pandavas including Arjuna were scared to death and Krishna planned to use treachery to bring him down as others were incapable of stopping him that day.
- Narayanastra of Ashwathama would have consumed the entire Pandava army including Arjuna but it was Krishna who revealed the secret of countering Narayanastra only then the Pandavas managed to escape from the wrath of the weapon.
- The supreme Agneyastra of Ashwathama would have again killed Arjuna and the entire Pandava army but was rendered futile due to Krishna as revealed by Vyasa to Ashwathama.
- He failed to counter the Brahmastras of Drona and Karna which resulted in blasting of his chariot but he was saved by Hanuman and Krishna.
- Nagastra of Karna would have beheaded Arjuna on 17th day but Krishna pressed down the chariot and prevented the arrow from hitting Arjuna,’ s neck.
- Arjuna accepted his inability to counter Bhargavastra and claims how can a dead man be victorious indicating had he been in the range of Bhargavastra he would be killed. It was Krishna who suggested Arjuna to retreat to the camp hoping Karna would be exhausted giving Arjuna a better chance to fight him.
However there is no scope of these events occuring. Because without Krishna Arjuna would have been kiolled by Bhagadatta on the 12th day.
But Krishna was not the only one protecting Arjuna. In case of Ashwamedha Yagya Jyadratha foot soldiers would have killed him but Saptarishis Saved him from certain death. There were Invisible forces protecting Arjuna because of him being on side of dharma. This plot Armour might give him an edge.