Mike Tyson is one of the best ever. But when they asked him if he could take on some of the current champions from Russia, he honestly replied that he didn't know because each generation of athlete get better with more scientific training, better coaching, better conditioning, better nutrition etc. You have to keep up with the times and can't rest on the laurels of past classical fighter stories and assume that will still work today.
The founders of many classical arts of the past would probably all get totally demolished by a modern ring fighter. That's not to say that classical arts have no benefit.
Real fighting often leads to real injuries where you have to give up any kind of martial art altogether. If you don't get injured, then probably it is not realistic fighting. How many martial artists really train martial arts for real fighting? If you want real fighting then train six months and then sign up for a war.
The Roman Gladiators did real combat but that may not sell well national television today. Most of us seem to be more civilized that that. If you really want to do ring fighting then you should train in the arts who are good at that.
Some of the top MMA people have a classical background actually but they had to train and train to make that stuff really work in the ring.
For fighting, you need a coach experienced in the type of fighting that you want to do. You can't just rely on empty talk that some martial art really works. For fun, fitness or for leaning classical martial arts for beauty and form and for a lifelong hobby then classical martial arts are the way to go.
Real combat is not pretty. Real combat ends someone’s life.