I felt Monroe could have been that piece, yeah. Install him as the starting center and top option (second option when IT is out there).
I think Monroe could have averaged at least 18-10 for the Celts and Stevens could find ways to make it work defensively.
Harris would have been a nice Plan B.
Certainly I didn't think Amir Johnson would be the big get.
That's fair, though I never liked Monroe for this team. The way he gets his 18 (didn't attempt one 3 all year, just a hair over half his fg's were unassisted, plays at a really slow pace, etc) coupled with the defensive atrociousness just never seemed best. He to me feels like the type of player a team spends on to spend money, because they are a name and sought after, even though the fit is wrong (in context for The Celtics --- Milwaukee I'm not totally sold on but makes a little more sense. He still seems like an outlier to how they want to play).
Harris feels like a move that at least has potential but that was likely going to take Millsap going to Orlando for them not to match (effectively taking him off the market).
I guess I don't find doing nothing big, when nothing big was really to be had or appropriate, to be too dismaying.
A lot of people complain about a purgatory of being in the middle but The Celtics are better off being ok this year with flexibility for the future and the ability to trade their way into an impact player in the near future (meaning as a this year alternative to free agency), than to be stuck in the even worse position of being committed financially for the long term to players who don't fit what they are going for.