I would assume letting GH go frees up some money to get a decent center who can defend the paint. Even Horford, if that's possible. Or maybe one of an army of bigs Atlanta now has.
The team has no defensive bigs, except for Williams and maybe Tacko. I don't know what Tacko's status is, but he should be kept with his unique vertical skills and his athleticism for his height. Williams fits the need, but he lacks the durability to be a dominant player. Maybe that's why he gets limited minutes.
I don't think this team needs any more small ball players. The two scorers they drafted are nice off the bench.
What's needed is a stronger inside game on defense. Maybe a combo of Williams and Tacko, used properly, can do that. Maybe Horford back or another defensive big. Defensive bigs are not that expensive.