I think there's definitely been significant improvement, and I'm not looking at the record, I'm basing it on how the team looks on both defense and offense.
First, their D is really good, especially with Horford and R Williams on the floor together. Remember early on when they couldn't get their switching schemes straight and were leaving shooters (eg Fournier) wide open from 3? That has been cleaned up dramatically and it looks like they're much better connected and are fully executing Udoka's system.
On offense, the ball movement is noticeably better. Early on in the season, even in the wins, they were relying on good 1-on-1 play from Tatum and Brown. Last night was emblematic of the way they've been trending. The ball was getting sprayed all over the floor and it showed with 31 assists. It looks dramatically different from even 2 weeks ago.
With all that said, look at the Eastern standings. The Celtics are very unlikely to crack the top 6 and avoid the play-in. Even with them playing better and with an easier schedule the rest of the way, the most likely way this season ends is with them winning a play-in game and then losing in the first round. That's fine for me. I fully expect them to package Horford, Richardson, and picks and go for a star in the offseason in a bid to contend next year.
I agree with those who are concerned by the short rotations and the lack of playing time for the young bench players. You can't play Tatum 38-40 minutes a night, or R Williams 30-35. And you've got to give some minutes to Langford, Nesmith, and Pritchard here and there.