I think it's all important. At this point they have cut TONS of drummers. It's already established that these drummers can play grooves. They've been through a challenge where they had to play straight pocket (the episode where they played American Girl), had a challende where they had to read music as written, and they also went through the 80's challenge where they had to recreate the drum parts exactly as done on the recordings. This week, the challenge was all about flash.
All aspects are needed as a touring drummer. I know that many R&B/pop touring bands will at some point during the show feature the musicians (at least the drummer). I would DEFINITELY think that will happen on Diddy's upcoming tour, since the musicians won't be faceless players, but they'll also be reality TV stars by that point and the crowd will want to see them to what they do best (at a Diddy concert, it's pretty safe to assume that the crowd in attendance will be made up of Diddy fans, most of whom are watching this show right now.) So if you're gonna have to solo on the tour, you need to have some chops in addition to the fundamentals. Like Nisan said to Diddy at the beginning of the show - at this point, everyone in the house is really good, so they just have to weed out whoever is the BEST. If the contest is about flash, which it was this week in the battles, then you better be able to bring the chops. The drummer that got cut didn't chowcase the chops that the other drummers had, so he lost this challenge.
It's just like any other competition reality show. I'm a fan of Top Chef on Bravo. On that show, every season someone who is one of the best overall chefs will get cut earlier than they should have because in the competition that given week they were subpar with a specific style, or whatever challenge they were presented with. It doesn't matter that they were great up until that point, or that they are good enough to win. On a reality show competition you have to be consistantly good in every challenge, every week.