I get the worry with Vucevic possibly being another Fournier here.
However, I think the guy needs a chance and some time. He even admitted in an interview a few days ago this is the first time he's been in a situation like this in his career and having to also adapt in the Mazzulla system. (Although idk, I thought he was with some good teams in the past like Orlando late 2010s, but maybe I'm misremembering?)
And remember, we loved Simons around the trade deadline and we love Luka Garza now. But most of this forum (including myself) thought those two were stiffs or meh players very early in the season. They took some time to grow/improve and adapted here. Now Garza looks like a legit backup big. Simons got better defensively too, to a playable level after looking toast early.
I'm sure they'll also try for a bigger fish in the offseason using Porzingis TPE and other resources, but I'd also be perfectly fine bringing back Vucevic on a reasonable MLE-type deal to play the Horford role. And he might be down for that too if he wants to contend.