Anyone who doubts MMA should walk into a real Brazilian jui jitsu dojo and tell them the same. You will be tapping out or choked unconscious quickly. When I was doing it 15 plus years ago I saw karate guy after karate guy come in and leave with their tail behind their legs. Jui jitsu is just submission wrestling. It has been tried for thousands of years. I don't care what you bench. A big bench doesn't mean you can throw a hard punch. It would help you getting out of an arm lock either.
U forget grappler can use all their tools for submission. Strikers can't. Can't poke, stomp, go for knee etc.
It's rather accepted to break the arm, leg or choke, but breaking the knee through a kick is a foul. Thrusting the neck, eyes, kicking the groin is llfe threatening though.
Remember that all the striking, grappling martial arts was founded in a much more rough era.
Can only blame our modern society that strikers can't use everything.