Athleticism is more important for the simple fact that skill/technique can be taught but athleticism cannot. Coaches can teach skills/technique. You can learn BJJ, kickboxing, boxing, you can learn the martial arts. Coaches can't teach athleticism. You can't teach a fighter to have fast twitch muscle fibers and be explosive.You can't teach speed. You can't teach reflexes. You can't teach Power. You gotta be born with it.
But at the same time, a fighter can have great technique/skills and overcome great athleticism + very good skill/technique. I look at boxers like Marquez and Pacquiao, where Pacquiao was clearly the better athlete but Marquez was better technically which allowed him to compete with Pacquiao.