The Yelich comparison makes it seem like you didn't read what I said. He was 26 and 27 during his MVP level seasons. Bellinger also got started a couple of years older than Guerrero. Age makes a big difference when it comes to predictions, which is why I brought it up.
Your comparable for weight are also imperfect and don't really add anything to the conversation. Miguel Cabrera is the obvious comp and you didn't even mention him. What about Tony Gwynn, Kirby Puckett, and Babe Ruth? His career path is not going to be defined by his previous weight.
We've seen many other lists like this, but look at the youngest players to hit 100 home runs, for example.
Mel Ott
Vladimir Guerrero Jr
Alex Rodriguez
Eddie Mathews
Bryce Harper
Andrew Jones
Johnny Bench
Miguel Cabrera
Tony Conigliaro
Albert Pujols
You'll get the same kind of list searching by any number of important indicators. I'm not saying he belongs in Cooperstown already or that MVP calibre players never regress. I'm saying that players who are this good at this age almost never fail to have Hall of Fame calibre careers. There's a big difference.