There's a jump to be made going from martial arts training to actual street fights. Some people are incapable of making that jump. For some of them it is physical. Training makes everyone better, but with striking in particular, there is an entry level of basic athleticism that is required IMHO. Some people simply don't have enough fast twitch capability to ever be effective. No matter how many years or what rank they attain. Some people lack the mentality. It's just not there. (these may be people that are more mentally healthy IMO.) That doesn't mean there is anything wrong with what they were training in. (although there are plenty of fraudulent MA instructors out there teaching BS). They just don't have that in them. Training isn't fighting. Even heavy contact training wearing gloves is different from what is going to happen bare knuckle/no rules/no ref/no mats. It's closer, but still not the same. You can't expect to be good at anything doing nothing but simulations. You will be better equipped than if you had done nothing, but no guarantees. And you can't train hardcore for ever. The idea is this is a life-long pursuit. There is a stage where going hard is valuable. The juice is worth the squeeze. But at some point, you have to back away from that. If you don't you are going to start carrying life-long physical damage with you. That becomes counter productive. You're crippling yourself and limiting future capability. I have been around mid 70 year olds that could still move. Still dangerous. Even with their max speed declining, their sense of timing and distance made them formidable. There is a LOT of value in going through the training and the various stages. And a lot of that value has NOTHING to do with fighting.
I'll shut up now.