I'm absolutely baffled by the idea that people would take a guy who can't defend at all. I don't mean he's a bad defender, he's one of the worst in the league, who cares if he's 6'7", he can't contain anything he's abysmal. He can't pass, he can't rebound, he can't drive. Last year he was basically the answer to the question... "What if Grant Williams was really bad at defense", that kind of player doesn't play in the playoffs (I mean look at MIA who had to bench Robinson).
Why would you want to use your one shot at taking on salary on that? Huerter for example is 7 years younger, better at almost everything (not quite as good at standstill 3s), on the ascent, he's not quite the 3pt shooter, but he's gaining and he does it on higher volume. Luke Kennard is better at everything (including shooting 3s), Gallinari is similarly a good case for being better at everything.
The TPE is the Celtics' best chance to add a player who can really help in the playoffs. Adding a guy who has 1 skill and will get played right out of the rotation would be terrible. Did we come out of the finals saying "man I wish we had a guy who hit 1-2 more 3s a game and sucked on Defense"? No, we came out of it saying, "we need another wing who can hit shots and pass the ball without breaking the defense"