I just don't see it as a given that Madar bulks up. First, he's been playing professionally since 2018. He has access to world class strength and conditioning training, and while 20 is still young, he's frail looking. His age 20 physique didn't look any different from age 19. Again, as a pro basketball player already, it's not like the NBA has some sort of proprietary secret sauce for strength training that Israel or other pro leagues don't have.
Secondly, not everyone has the frame to add weight. Poku, Shaun Livingston, Tayshaun Prince, Rondo...there's no shortage of examples of players who are just naturally skinny. Skeletal structure, bone density- some players just don't have the frame to add weight. When I see Madar, I see that same sort of body type. I hope he adds bulk, but I don't see it as a given.
I mean, I've been wrong a million and one times, and I'm sure I'll be wrong a million and one more. It's entirely possible Yam will be fine physically, or that his size won'thold him back. I hope he makes it. But I reject the notion that it's a given that he'll easily bulk up once he hits the states or ages. It doesn't work that way for everyone.