Battle rap doesnt have to be popular to have saved hiphop.
Im not saying it did or didn't, but saying 99% of ppl don't follow it don't mean shit. You don't need a vast majority, all you need is a small few to control the massess.
Case in point would be if the top of the current food chain, I.e j.cole, drake, kendrick are heavily influenced by battle rap, then it creates a chain reaction to where others copying those at the top, will change how they rap.
Put it this way, snap rap and shit dominated 2005-2007. Let's say hip hop was dying, over the next few years ppl like Charles hamilton, drake, kendrick, cole etc come into the game. While not all of them battle rap, they are familiar with it and watch battles on YouTube. So when they write their songs they add some bars and focus on lyrics wayy more than ppl did in snap era.
So now a young kid deciding to be a rapper, hears drake or kendrick or lupe actually spitting witty lyrics or dope lines, and they write their rhymes like that...now the young kid may not even know a thing about battle rap, but he was influenced by the guys like drake that are big fans, so regardless it has its effect.
Now before ppl tell me drake isn't a Battler and all that, it doesn't matter. Or that this didn't happen...I'm not saying it did. Alls I'm saying is its very possible that battle rap did have an effect even if never became mainstream itself.