So Karna single handedly defeated the entire army of Chitrasena’s army.

Why did Karna get defeated by Gandharvas while Arjuna defeated them quite easily? Arjuna defeated them quite easily due to a very simple reason. Let's see what actually happened between Karna and the Gandharvas. They had three different encounters. ‘On seeing the gandharvas swiftly descend on them with raised weapons, the sons of Dhritarashtra could be seen to flee in all the directions. On seeing that the sons of Dhritarashtra were fleeing from the field of battle, the brave Vaikartana was the only one who wasn’t reluctant to do battle. On seeing the great army of gandharvas descend on him, Radheya repulsed them with a mighty shower of arrows. With great lightness of hand, the suta’s son killed hundreds of gandharvas with kshurapras,34 vishikhas,35 bhallas,36 vatsadantas37 and iron arrows. The maharatha sliced off the heads of many gandharvas and in a short while, dispersed all of Chitrasena’s army. So Karna single handedly defeated the entire army of Chitrasena’s army. Although the gandharvas were killed by the intelligent son of the suta, they returned again in hundreds and thousands. In a short instant, the earth was covered with gandharvas and Chitrasena’s soldiers descended with great force. Then King Duryodhana, Shakuni Soubala, Duhshasana, Vikarna and other sons of Dhritarashtra ascended chariots that screeched like Garuda and began to kill those soldiers. They fought again, placing Karna at the forefront. There was the giant roar of chariots and the stamping of the feet of horses. Supporting Vaikartana, they repulsed the gandharvas. Then all the gandharvas descended on the Kouravas and the battle that raged was extremely terrible. It made the body hair stand up. Oppressed by the arrows, the gandharvas began to wilt. On seeing that the gandharvas were suffering, the Kouravyas roared loudly. Karna defeated the Gandharvas again, which finally angered Chitrasena and he started using maya to counter the Kourava army. On seeing that the gandharvas were frightened, Chitrasena was overcome with anger. He angrily flew up from his seat, resolving to kill them. That brave one began to fight with weapons of maya, following wonderful paths. The Kouravyas were bewildered because of Chitrasena’s maya. O descendant of the Bharata lineage! It seemed as if each one of Dhritrarashtra’s sons was assailed and surrounded by ten gandharvas. Contrary to popular belief, Karna wasn’t not afffected by Chitrasena’s maya and he was the only one who stood there unaffected and kept fighting. Dhritarashtra were being destroyed. O king! Vaikartana Karna was the only one who stood immobile like a mountain. Duryodhana, Karna and Shakuni Soubala were severely wounded in the field of battle, but kept fighting the gandharvas. With a desire to kill Karna in battle, hundreds and thousands of gandharvas rushed collectively towards him. With a desire to kill the son of the suta, the immensely strong ones surrounded him from all sides, with swords, javelins, spears and maces. Some sliced off the yoke, others brought down the flagpole. Some brought down the shafts, the horses and the charioteer. Some sliced down the umbrella, others the fenders and the diadem. In many thousands, the gandharvas shattered the chariot. Holding a sword and a shield in his hand, the son of the suta jumped down from the chariot. He leapt onto Vikarna’s chariot and whipped the horses, so that he might escape.’ So basically Karna did defeat the Gandharvas atleast twice and even countered Chitrasena’s maya and only strategically retreated after looking at the situation, believing all hope is lost. Arjuna on the other hand countered Chitrasena's illusion and defeated him in battle. This would prove his superiority right? Here's what Chitrasena's said: Chitrasena was fighting mildly with Arjuna, he never wanted to cause any harm to the Pandavas. As we see The Gandharvas never wanted to kill Arjuna, they only wanted to kill Duryodhana and Karna. So in summary: Karna defeated hundreds of thousands of Gandharvas and shattered their entire fleet twice Chitrasena realises this and starts using illusion warfare which gives him and upper hand. Karna is still majorly unaffected but still retreats from the battlefield. Arjuna and the other Pandavas enter the battle as a team and start beating the Gandharvas. Arjuna counters the illusion. Chitrasena reveals that he was only here to protect Arjuna, the Gandharvas were only there to kill or defeat Duryodhana and Karna. It was not a real battle. So it was basically a rigged match. Indra orchestrated the whole thing for the humiliation.