I share your concerns. I'm not excited about the idea of giving up the farm to try and pair Kyrie and Davis. I would not be confident that Davis would stay in that scenario.
Just to play devil's advocate, though, here's a list of all the players who made All-NBA this season, with the year that they will enter Unrestricted Free Agency and the age they will be in that year:
Curry (2022, age 34)
Harden (2023, age 34)
Giannis (2021, age 26)
George (2022, age 32)
Jokic (2023, age 28)
Lillard (2021, age 31)
Kyrie (2019, age 27)
Durant (2019, age 31)
Kawhi (2019, age 28)
Embiid (2023, age 28)
Kemba (2019, age 29)
Westbrook (2023, age 34)
Griffin (2022, age 33)
LeBron (2022, age 37)
Gobert (2021, age 29)
Setting aside the 2019 names, Giannis and Rudy Gobert are the only guys on this list entering UFA under age 30 in the next couple of years.
Does anybody think that the Bucks are going to look to trade Giannis next summer? Assuming they won't, do you think he's going to look at Boston in free agency in 2021?
I think it's fair to say that Rudy Gobert isn't a guy who by himself makes a good team into a contender. I don't think he's the answer, even if we assume he could be available in a year.
The bottom line, I think, is that if you are hoping for the Celts to add a MVP caliber player via trade or free agency, that player is either somebody who is nowhere close to playing at that level right now or is a guy who hasn't entered the league yet.
All of this is why I think Ainge is going to be aggressive and take risks this summer.