Well, even if it's just a UI kinda thing, it's still something that can be employed by him and then counts as his own merit. It's not because that such reaction speed isn't totally reflective on battle power that his feats are to be diminished or ignored. Roshi also defeated Kasheral who read his BP as insignificant to the performance he was putting, so Roshi is > Kasheral despite being inferior battle power wise much the same way Merus might not be all that BP wise but performance-wise, effectivity-wise he's relevant to Goku's strongest states, which is what matters.