IMO if Royce was really serious about combat sports he should have chosen boxing. You don't have to worry about the wrestlers/bjj experts and at that size and especially in the heavyweight division you can get away without having much (if any) of an amateur career.
Deontay Wilder for example is one of the worst boxers I've ever seen in my life from a skills standpoint, yet he's considered the top 1 or 2 best heavyweights on the planet because of his power and chin. (he did have 30ish amateur fights).
Another local example would be Tye Fields from a decade ago. Tye was a local DSM guy who went from basketball to boxing and won a decent number of fights despite his raw boxing skills. He was a big guy who hit hard and he made a little bit of money along the way.
You are spot on sir, with both the Deontay Wilder & Tye Fields examples. Deontay Wilder is undefeated, knocked out every person he's ever faced (except in his last fight against Tyson Fury but the ref's 10 count in that last round seem awfully slow/generous to me) but is NOT a boxer. He's an athlete that has absolute insane power and can take a punch himself.
With Tye Fields, you're looking at another athlete who's just bigger and stronger than everyone else he faced on the local circuit (I attended 2 of his fights live). It didn't work out the same way for Tye as it did for Deontay Wilder when the level of competition was raised but I agree with your comparisons.
I'm in the minority here but I think Royce could actually make a nice little career for himself in MMA. If he was any other weight class other than heavyweight, I think it would be a different story, but like others have mentioned on this thread, the HWY division only has a couple true submission threats but the top 10 guys in the world are mainly strikers. With Royce's athleticism, if he can get his conditioning right and actually be able to take a punch (this will be what it all actually boils down to), then he can be successful and make a nice living in the sport.