Basically since Ainge made the Nets trade, has tried to win, while also building for the future and that failure to pick a direction caused him to harm the title odds of both paths.
I disagree with this pretty strongly.
Like any smart GM, Ainge has set his franchise up to have multiple paths to follow toward success, rather than placing all of the team's resources on one plan.
Ainge spent most of the period between 2014 and 2017 piling up assets to make a move. There were potentially some opportunities for guys like George and Butler, but nothing that was a slam dunk because it was never really possible to get those guys with more than a single season left on his deal.
Thanks to the IT trade working out super well and Brad being a very good coach, the Celts were still competitive during that asset compilation period. That competitiveness allowed the team to sign Al Horford in 2016 and then Hayward in 2017.
Danny managed to trade for Kyrie Irving, a B-Tier star who had shown some MVP level upside during the 2016 playoff run, without trading away any of his best assets. This then set up the team to contend for a couple years with Kyrie, Hayward, and Horford, while leaving the door open for an even bigger deal for the next major name to become available.
We now know that Ainge had Anthony Davis on his mind for several years before Davis ever became available. I think it's pretty obvious now that the idea was that the team would thrive with Kyrie, Hayward, and Horford, leading Kyrie to want to stick around, and then Kyrie's cache as a star would give the Celts a chance to convince AD to want to come here. Trading for AD was supposed to be Ainge's follow-up to the KG trade. The major headline grabbing move that would change the NBA landscape and lead directly to Banner 18.
Unfortunately, the Hayward injury basically ruined all of those plans. The team still made the ECF in 2018, but that run actually threw off the plans even further in some respects because it created a rift between Irving (who didn't participate in that run) and the younger guys who introduced themselves to a national audience. It also made it that much harder to consider trading Tatum and Brown given what they'd shown.
This all culminated with Kyrie checking out almost a full year before he actually left in free agency, and Davis signing with Klutch and deciding he wanted to be a Laker over a year before his team was really willing to trade him.
Despite all of this, the Celts were still in a great position to transition to building around Tatum and Brown. They made the ECF yet again this summer despite not looking like a roster that would be favored to win a second round series as recently as last October.
The bottom line is that if Ainge had "chosen a direction" as you seem to suggest he should have done, there's a good chance that the Celtics would be in a much worse position now. Ainge could have easily gone all-in trading for a guy like Butler, Kawhi, or George, only to have that guy leave after one season. The team could have likewise traded for Davis, gotten one half-hearted season from him knowing that he was never planning to stay, and then watched him leave.
Many franchises would have simply been crippled by an injury like the one Hayward sustained. Thanks to Danny Ainge decidedly NOT putting too much emphasis on one plan or direction, the Celts have been able to shift gears and are now poised to remain among the upper echelon of teams while building around a 22 year old All-NBA talent and a 23 year old perennial All-Star type talent.
I guarantee that the same people complaining that Ainge didn't "choose a direction" would have excoriated him if he
(a) used all his trade assets in the mid-2010s to go after a superstar or two and that player left in FA before winning a title or
(b) traded away / chose not to sign any vets and focused on developing the young players, resulting in several 1st and 2nd round exits in a row.