I haven't read the books, but honestly I never got the impression Robb Stark was a main character. He seemed far less important than Arya, Brann
He was not, he was not a narrator character. Hint the point of views ( narrators) are the important ones as I see it.
Keep in mind the prophecy of the land, which the series has only hinted at through Melisandre
"There will come a day after a long summer when the stars bleed and the cold breath of darkness falls heavy on the world. In this dread hour a warrior shall draw from the fire a burning sword. And that sword shall be Lightbringer, the Red Sword of Heroes, and he who clasps it shall be Azor Ahai come again, and the darkness shall flee before him."
and this
Azor Ahai shall be born again amidst smoke and salt to wake dragons out of stone
Melisandre thinks it is Stannis. A lot of folk think this means Daeneyrs and some think it is Jon. But the prophecy in the book implies a rebirth of some type. Jon may well be a Targaryen as well. Recall he is a
Edited for profanity. Please do not do it again. but we never know the circumstances. Some think Rhaegar Targaryen is the father and Lyanna Stark was his mother and Ned raised him as his own. That would make Daenyrs his aunt.
Rob never was a main character. This is loosely based off the war or roses. The Lancasters vs York was that fight here we have the Lannisters and Starks. But all this war between the family is action that is not as important as the prophecy and the Others.
Whomever fulfills this is the most important character.