Not getting all the crossfit love TBH. An outlet for gym monkeys to willy wave wouldn’t be the top of my list for the OP’s question.
I think you have to define the question some more. Is “fittest” ability to be competitive at the highest levels in multiple sports, in multiple sports requiring very different attributes?
For me I’d define it as best survivability if the apocalyse came? 🙂 I.e. genuinely useful, rounded “fitness”, rather than being too specific or requiring certain technical sporting ability. I think the special forces type person would be top of my list if there is a sport consisting of this type of nutter superhuman. Extremely well rounded physically, extreme endurance, extreme discipline, mental toughness, decision making under extreme pressure. They may not have the technical sporting ability for a lot of events/ sports but I’m sure they’d do just fine in the scenario I’d use to find the “fittest”. I guess this is the wilderness/ ultra endurance/ exploring type “sports”men and women then for me