Queta is not a superstar big, so you need another big man period. In the past 5-6 years, the teams that have won it all either have a great duo (Ibaka-Gasol, KP-Horford, Chet-Hartenstein), or a superstar big (Davis, Jokic, Giannis). Even this year, it'll be Wemby, or KAT-Robinson.
The Celtics were heavily exposed on that front in the Sixers series when Embiid returned, and they were going to be in the Knicks series too. Queta is a solid big man, but Vucevic/Garza were basically nonfactors or terrible so it left a void. If they can pair Queta with another capable guy, it should help the team a lot.
PG would be nice but I don't prioritize that. Of course, adding both would be ideal. Dump Hauser, let Baylor/Hugo play more and use some of those savings to acquire one of the two. The other can be acquired via TPE or a White trade.
Sorry but the more I watch these Finals and even the ECF/WCF, the more I feel the Celtics are just not even close to these other teams in the frontcourt. Again, I like Queta and he's gonna continue to grow/improve, but they absolutely need another guy in the frontcourt. And I doubt Amari Williams will be close next season. Sure, the playstyle and 3-point philosophy needs to be adjusted, but that won't matter a ton either if the frontcourt isn't revamped.