Not sure I get this post, at all.
Marcus Smart has great size for a guard. Granted he's not super quick but he is very strong and a good two foot leaper.
Jaylen is one of the best athletes in the league, seven foot wingspan.
Langford is big for a guard, again near seven foot wingspan. He is very fluid, has an excellent first step. Not a huge leaper but he's not a liability there either.
Tatum has all sorts of length, he's not an elite athlete but he's at least average for the SF.
R Williams is an elite athlete with elite length.
G Williams I will grant you, undersized and ground bound. But he's a late first intangibles guy.
I think the problem you really have is the complete lack of big men on the roster, and the guys who will probably play power forward (G Williams, Tatum, Hayward) are either a little short or lack bulk. But we arent done yet, and the rets of the team is pretty long and athletic.