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 **** 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.
That's interesting about Jon Snow. I listened to a podcast with the show runners and they were talking about their first meeting with G.R.R Martin. Martin wanted to test them on whether or not they were actually fans and had read the books... so his question to them was "Who is Jon Snow's real mother?"... apparently it was a bit of a trick question, because the books had not yet revealed who his real mother was... but they apparently guessed correctly based on some hunches. So I've been aware that there is some mystery as to who his real mother is... and I had to assume it was a Targaryen otherwise it wouldn't be all that compelling. But I hadn't considered the possibility that Eddard isn't his real father. Interesting. But that does make sense... I had read on the wiki that part of the lead-up to the rebellion was that Rhager Targaryen had abducted Eddard's sister.
Probably don't say any more on that... seems like book spoiler territory.
There are a lot of incredible theories in game of thrones.
Pretty complicated stuff so I wont delve into it here but if any of yall are really into the books and theories you should head over to "a forum of ice and fire". Dont do that if you have not read the books, though, as stuff will definitely be spoilt.
I really love the next book because it really delves into a lot of the mystery and unexplained in Westeros.
The Dunk and Egg stories are also excellent short stories based about 100 years before the current game of thrones events that are a nice reprieve from the intense heartbreak of the main books while also revealing some mysterious prophecy stuff.