Danny has been a top tier GM.
I don't think we should dismiss the OP's primary concern, though. I think it's an interesting question: is Danny too cautious lately?
I would posit a different frame for this:
"Is it possible that Danny is somewhat more patient as a GM now that he's built a contender, torn that contender down once the window was closed, and then put together a good-but-not-great team to replace it?
My feeling is that the answer might be yes.
But .... maybe that's not a bad thing.
Look, the first time Ainge built a contender, it came together almost all at once. It was a whirlwind summer, and then the team stormed the regular season, won a title in their first run, and then looked unstoppable the following year. Until, that is, Kevin Garnett injured his knee. After that, the team remained competitive, even coming within one quarter of a second title, but they were never the same juggernaut that they were before KG got hurt.
What I suggest is that perhaps what Ainge took away from the experience of the KG years was that a contender is a fragile thing. One title won does not guarantee later title wins.
I think perhaps Ainge wants to build a contender very badly, but even more, he wants to build a team that can sustain success over a longer period of time. Because Ainge doesn't just want to bring Banner 18 to the Celts. He wants to bring Banners 19, 20 and perhaps more after that. He doesn't want to build a team that can be the 2004 Pistons (the KG Celts compare strongly to that group) or the 2011 Mavs. He wants to build a team that sit atop the league for a decade, or more.
To that end, he is looking for ways to maximize the talent on the team, but he is focused on building a culture, as Boris explained. Furthermore, I think he's focused on ways to build up a talent base that is sustainable, with a cache of assets sufficient to keep the roster well stocked with affordable talent. Danny does not want to be one knee injury away from his painstakingly constructed contender to turn into a second tier also-ran.
Ainge has already joined the ranks of GMs that built a title-winner. Now he wants to be one of the select few who have built a dynasty.