I was re-reading the 5th book recently and i realized that Neville was using his Dads wand up to going to the Ministry of Magic. As we learn in book 7, the wands allegiance may not have been towards Neville, which explains why he does so poor in school the first five years.
Before he gets his wand, in OOTP, Harry first notices a change in Neville just after the newspapers report that Bellatrix has broken out of Azkaban. Harry noticed Neville throwing his all into his DA sessions, and that he was improving more quickly.
Then, before he got his new wand, Neville was the ONLY student at the battle at the Ministry of magic who remained conscious the whole time. I believe this says that even without the right wand, Neville was still a strong fighter.
Following getting a new wand in book 6, we see him fighting Death Eaters in Book 6 and raising a coup in Hogwarts in Book 7, both of which I doubt he could do effectively in Book 5 and prior.
For all we know, if Neville had the right tools, he may be just as skilled at Defense against the Dark Arts as Harry was! He certainly had the lineage for it considering his parents were aurors.