There were many warriors in Mahabharata. Barbarik was a greater warrior than Karna but he did not get a chance to fight the war. Ashwatthama was also a great warrior but his greatness ended when he killed the sleeping Pandava sons. Eklavya can also be considered great but he also did not fight the war, then how will his greatness be proved? We cannot include Drona, Bhishma and Shri Krishna in this because they were Gods.
In fact, Karna was the best warrior who established himself as a great warrior despite adverse circumstances and that too as per Dharma. Let us know those facts about Karna due to which he can be considered a great warrior.
Arjun had the lord of the world to support him but Karna had only Duryodhana to support him. Arjuna was completely dependent on Shri Krishna while Duryodhana himself was dependent on Karna.
Drona did not give the complete education to Karna that he had given to the Pandavas or Kauravas. Nevertheless, Karna had obtained the remaining teachings from Parashurama by deceit. If Karna was not as capable as Arjun, Lord Parashurama would not have been ready to teach Karna.
Apart from being a true friend, Karna was also a generous person. Lord Krishna himself confirms that there is no greater donor than Karna. When Karna came to know who his mother was and who his brother was, he still followed the religion of friendship.
As per the plan of Shri Krishna, Arjun’s father Indra snatched away Karna’s armor and earrings by deceit, despite this, Karna fought the war like a warrior.