Chara wasn't good until he was like 24 or 25.
Yep, and if you go look up the reviews of his first couple of years in the league as an Islander, they'll read similar to Rempe in that he was a HORRIBLE skater. Looked like bambi on ice, turns like a mac truck, etc. etc.
This is not to say that Rempe can be like Chara or anybody else. Rather it's to say 1) Other big players have had the same issues as him at his age and significant improvement is not unheard of. 2) His learning/improving should be done below the NHL level to maximize any potential that there may be.
Honestly, having him up with the Rangers, playing 4 minutes, every other game, is just as much a disservice to him as it is to the Rangers.