“I define functional as strength that’s there from any angle.” Thats a bit of a dumb definition. Personally I think it is a retarded term but here is what’s wrong with your definition, strength isn’t just angle specific it is also lift/movement specific.
Everything carries over to a certain extent but you are misguided in thinking these guys could bench press even moderatly impressive numbers to someone who has put in work in the bench, deadlift, and squat. Yes there are stories about gymnasts benching twice their bodyweight the first and you know what I have never seen it. Maybe some elite gymnasts that are genetic freaks, maybe.
These guys are strong sure, in what they are doing, and powerlifters are strong in their own right, so are olympic lifters, and so are many other sports. But to say that one is more “functional” than the other is idiotic. Whats more functional at 170 a 350 bench, a 300 jerk, lifting a 300lbs stone, or an iron cross? Functional for what? is the right answer.