Janaki...May be Arjun did not lead per se, because the brothers always obeyed Yudi,,,,one of the mega reasons why no one really stopped (objected but not strongly maybe) to them being or Draupadi being staked at the dice game!
Arjun is portrayed as leader because it was established even during Kurukshetra that if there was no Arjun, there can be win of Pandavas...one of the major reasons why Chakravyuh was framed and Jayadradha could invoke his boon for one day!! Why the whole Kaurav sena actually tried to protect Jayadradha the next day because they knew if Arjun took self immolation, they had won the war hands down!!
Yes even I had my doubts why Arjun and Duri were shown nose to nose (literally😆) in the promo because I always thought that it was Bheema and Duri at war all the time!!
But it came out that all through out the Pandava life time, Bheema had been more the saviour and Arjuna more the fighter...Bheema ofcourse fought Bakasura and Hidimb and Kinchak ofcourse...but generally Bheem is associated with saving...like from the Lakshagruh and all other times...
Arjun was more like the prize fighter...Druapadi and ofcourse war with Drupad..and then Virata fight with Hastinapur warriors...He lone handedly brought them victory!!
May be thats why!!