The ages of them is the big difference here, I bet
Sixto was 25, Mitchell 27, Belle 27, Clark 31, Rocky was 24. So for half of them sure, but Rocky and Sixto were around the same age range. But either way I'm not sure how age is really relevant here. Harper could develop more HR power as he ages, but he's unlikely to have a slugging % much higher than he has now. So you are talking about his average staying in the same ballpark, which I highly doubt.
I mean, due to the age he was when coming up along with his talent level and the lower offense of this era I'd put better odds on him making the HOF than not if he stays healthy, but you guys are making definite best player in baseball comparisons and Lebron James comparisons, which is an entirely different ballgame. Lebron has been the best player in basketball for at least a 10 year stretch at a time.
Ken Griffey jr was doing similar stuff at a similar age as Harper and even he didn't turn into a Lebron James of baseball. Griffey jr wasn't even the best player in baseball for good portions of his career. It's extremely hard to be that consistent.