There's another factor here, expanding on the defensive upside of Gay at SF and JT at PF. Obviously it allows a full-sized starting lineup across the frontline and protects Cuz defensively, as well as gives us a better chance at matching up against the PF's of the Western Conf, which make no mistake about it is stacked with PF's.
But going beyond that, Gay is a SF, through and through. JT is a 4/5. Williams however can swing either way, so to have his versatility off the bench would be a luxury. Cuz gets in foul trouble, move JT to the 5, Williams to the 4 and continue with Gay at the 3. Gay gets in foul trouble, straight swap with Williams. JT gets in foul trouble, bring on Williams. At least at that point one hope is JT has prevented the opposing PF from getting in an early rhythm and I don't know how anyone would question what he adds to this team defensively after the job he did on Dirk last night as one example.
Going even further, PDA has said he sees Gray as stepping in and playing center, even allowing Cuz to move to the 4 at times. So we have a backup center in PDA's mind, meaning we don't need JT on the bench as our only other true big backing up Cuz.
And adding onto that, with IT starting we don't have an offensive spark off the bench. Bring JT off the bench we continue without a spark. Here we have Williams who has shown he can score as well as guard multiple positions. His energetic, up and down style fits more as a bench spark as well given our team's needs.
And oh, btw, start IT/MLM/Gay/Williams/Cuz and try to tell me there won't be at least some fighting for shots and 1-2 players having their effectiveness being negated to a certain extent. JT is a role player in the truest sense. He doesn't steal shots from others. Doesn't step on toes.
It makes too much sense to have a depth chart as follows:
Cuz/Gray
JT/Williams/Landry
Gay/Williams
Anything else and I'll immediately start worrying about Denver part deux. Anything else and you're looking too much at exciting, race horse basketball and ignoring the other side of the ball as well as what has proven to win vs not win in this league. As has been stated multiple times, unless you have Lebron, the greatest physical freak of his generation, going small does not work if your priority is building a winner. It's a gimmick. It's one thing to go small at times in games but quite another to plan on going small from the jump. You've got to look past the sexy fast breaks, lobs off the glass and open court dunks and realize that's really only a fraction of this game. It doesn't win and that's been shown time and time again. GS figured that out and invested in Bogut, waiting well over a season for him to heal up and then went after Iggy. And no, when everyone is healthy they don't bench Lee and instead go with the more athletic and up tempo combo of Steph/Klay/Iggy/Barnes/Bogut. No, they stay big and bring Barnes off the bench. Why? Defense wins. Doc is trying to change the culture in LA away from Lob City as well. Why? Defense wins. Even the most well known run & gun teams realize this at a certain point.