Well for one Chris Kreider. He regularly takes place in the fastest skater competition in the all star game and tends to rank pretty high. Alex Ovechkin and Josh Anderson are pretty fast as well. I would need to do some research to offer a more comprehensive list but there are certainly very fast players both in the league currently and in the past that have been over 220 lbs.
As for physical maturity just because he is more physically mature than other prospects doesn't mean he has reached his genetic athletic potential. I think it is a bit of a misconception when evaluating prospects to assume that just because a prospect is more physically developed than other prospects and that there isn't a lot more room for them to become substantially more physically developed.
Boucher is 19 years old and was listed at 6'1 205 lbs at 18 years old when he was drafted. He could get a lot heavier and substantially more powerful.
The average age of peak performance for male Olympic weightlifters is 26 years old.
Performance Development From Youth to Senior and Age of Peak Performance in Olympic Weightlifting.
The average age of peak performance for powerlifters is 34 years old.
At what age are we the strongest? Surprising truth
How old are the best athletes in weightlifting and powerlifting
According to some of the research there the average age of peak performance for specific lifts is:
Snatch (26.4 years), Clean & Jerk (26.1 years), Bench Press (34.3 years), Squat (34.1 years) and Deadlift (33.5 years)
If the most powerful athletes in the world who dedicate themselves full time to power development don't peak in performance until those age ranges then it doesn't make sense to assume that an 18 or 19 year old hockey player has peaked or come close to peaking their power potential.
The fact that Boucher is so dedicated to physical development makes him more likely to reach his peak power potential than others who aren't as dedicated. It is also quite likely that his gap in power relative to his peers at a similar age will likely remain the same and potentially grow larger over the course of his career.