Lanky with long arms for the weight class is one thing like izzy jon or alex, but 6'7" and cut to 155 is absolutely unheard of, at least to me. Like, it looks absolutely comical on film.
Chet and Wemby are still super young though, they have time to fill their frames out more. Giannis came in at 190 and gained 50lbs his first few years. Anthony Davis put on like 30lbs.
Wemby seems like he'll have the better chance to fill out just by virtue of being a bigger dude, Chet is built a bit slimmer too IMO
by "fill out their frames" you mean "put on muscle"? then yeah, those young NBA guys certainly can and it would help them to put on twenty or thirty pounds at their position. but, if they were mma fighters trying to make a certain weight class, let's get this straight: their frames are not going to get any bigger. they are done growing bone wise. so, if they chose as they go older to keep their muscle mass downs through a mixture of a controlled diet and cardio training w/out weight training, not to mention a minor weight cut, they could not only make 205 but possible even 185 if they wanted to be extreme with it.
the only reason mma guys and boxers keep their weights so trim is because they compete in a weight class sport and it helps to keep trim as it makes the weight cuts easier. but also make no mistake about it: most athletes in other sports are carrying a lot of muscle and could lose a lot of that and fight at lower weight classes if they wanted to. there are
very few men on this planet, including large framed high level athletes, that couldn't make 205 if they lost a lot of muscle, went on a controlled diet and did a lot of cardio and without weight training. and even guys like Shaquill O'Neil could still make 265 if they did the same thing and kept their BMI's down (with that said, I favor the heavyweight cap in mma being 285)
and also for the record: height is only one part of size. I know guys that are north of 6'8'' tall that could fight at 155
if not 145 . we call those kinds of guys "slim" for a reason, because they are built like this:
being 6'9'' and with a frame like that, does not make a man a "giant". on the other hand a guy like Antonio Silva is 6'3'' with a frame like this, who had to lose a lot of muscle to be able to cut to 265 (used to fight at over 300 pounds in Japan):
So, height is only part of a man's size,
along with robustness/width of bones, bone density, leg to torso ratio (some men have longer legs and shortor torso (like Hicham El Guerrouj), while others have longer torso and shorter legs (like Stipe Miocic)), width of clavicles (that is, how wide the bones of the shoulders are), width of rib cage, width of the waste (mesomorphic men have wider clavicles than waste; but meso-endomorphic men still have wide clavicles, but also a comparatively wide waste for instance, meaning they are not as efficient runners but will be comparatively heavier), size of the head, etc. size of the feet and hands as well.
also with that said: since most men are around average when it comes to all the other things I listed,
on average, a taller man will weight more at any given BMI, than a shorter man. on average with all other things being equal, every inch of height ads anywhere from five to ten pounds of weight (closer to five for most but for larger framed men in can be more like ten)