Rinzel does look thicker than he did when he was drafted. Says he's up to 185-187 right now and pushing for 190 this season (when he got drafted he was around 177-180 I believe). He wants to get to 195 next year.
Looking at the weights of NHLers around 6'5" (minus goalies), we're looking at about 220lbs as Sam's target weight by the time he hopefully consistently gets on NHL ice.
Let's say Sam is 190lbs right now. He just turned 19 (June 25). Let's give him 4 summers to train and gain ~30lbs. Big DMen take longer to develop. That's 7 pounds of muscle per year. It's doable by the time Sam's 22 years old.
6'5 220lbs is legitimate NHL weight for a big DMen. As a comparable, Alex Vlasic was listed at 211lbs (6'6") 2 years ago at Boston University (198lbs when drafted). A year later (Oct '22) and in the Hawks training regimen/system, he was 220lbs at 21 years of age. I'm sure he's gained some more muscle at 22.
So yeah ... 7lbs per summer for Rinzel is more than realistic by the time he is Hawks ready.