This is such a good question. Neville and Harry had a similar upbringing but in reverse. Harry had magical signs early and his horrible aunt and uncle tried to suppress it, added with the bullying. Meanwhile, Neville didn't display magical signs early and he experienced trauma from relatives trying to force the magic out of him until it finally happened. But Neville had pressure from his parent's reputation with the constant comparisons. Harry was unaware and only left to be amazed and proud with how his parents were because his relatives spoke ill of them out of jealously.

Harry had a natural talent for flying and other skills that gave him confidence along with his best friends. Neville's talent was Herbology and he didn't have a dedicated close group of friends until the DA with Luna and Ginny through Harry. Who knows? With Neville having the scar and growing up in the wizarding world unlike Harry, he might not have been as humble. Maybe he would have had a slight ego that would've tempted him into Slytherin? That was one of the reasons why Dumbledore didn't have Harry grow up in the wizarding community with people who would've treated him better. But with his grandmother, maybe Neville still would've been reminded of his legacy and had the insecurity embedded.

It's hard to say. Neville gained confidence over time and was trusted with the task of killing off Nagini, which brought everything full circle. I think Neville could've had as much potential being the chosen one and would've succeeded too. But with even more internal conflict, instead of just living up to his parent's reputation but also the reputation of what he could do as a baby. All the information to him would've been shared differently, especially if he didn't gain trustful friends as early as Harry did.