I'm hoping to make the OP realise that by comparing boxing to tennis, he is illustrating exactly why the point he's been trying to prove in this thread is wrong..
If tennis is all about talent, then why couldn't somebody with a natural talent for tennis take it up age 21 and compete with Nadal?
Truth is, tennis isn't primarily about talent, it's about taking up a very basic, simple sport at a young age, then spending years and years repetitively practising the same basic moves, in the same situations, over and over again, until they become second nature and you can respond instinctively and instantly without having to think about it, to whatever your opponent does. Obviously,there is an element of natural ability, aka talent, involved, but years of repetitive practice, from childhood on, under the supervision of an experienced professional coach, is the most important factor.
And if boxing is all about physical attributes, then how could somebody like Fabio Wardley take up boxing at age 21 and become a world champion in a division full of guys with the same physical attributes as him?
Answer: The same reason why Usyk could first set foot in a boxing gym at the of 15 and become world amateur champ and Olympic gold medalist 6 years later. And 6 years after that, he wins his first world title as a pro. Obviously, repetitive training to build up fitness, muscle memory and instinctive reactions is also important in boxing, but talent matters more in boxing than in tennis, which is why naturally talented guys like Fabio and Usyk can progress so much faster in boxing than in tennis.
I get it. I just decided to do it differently. But of course, a lot can be said, and I think you can get more practical skills from boxing than from tennis, for example. Is boxing the hardest or the most demanding sport? It depends on what defines those two. Because gymnastics is harder and more demanding on the body in one way. In another, it is boxing that is tougher for the body, because of the damage.
Taekwondo also requires more skills; in the end it creates worse quality fighters than boxing, I'd say.