I keep going round in circles on male dating sites that focus specifically on fitness and I'd rather ask than guess. It is worth separating out the male side of the app here, because with fitness, it is worth checking how often the same faces reappear before you look at the size of the database. The sports sites angle is worse, because what decides it is how often the same faces reappear, not how slick the interface looks.
Fitness sports is where I would start, since the ratio of matches to conversations does more work than the number of features listed. For fitness sports in particular, how quickly the inbox fills matters more than the follower count on their socials, on the evidence I have.
Look closely at fitness sports and the deciding factor is the churn on new sign-ups, though I'd want someone to check me on this. Put male dating sites that focus specifically on fitness beside anything comparable and the platform surfaces profiles far outside your radius, which makes any straight comparison unreliable. Specifics about fitness welcome — vague reassurance less so.