Yes improvements have certainly been made: https://www.youtube.com/watch?v=4TxPRlnnBLoBut ultimately, the thing about 3D anime with toon shaders, is that when theyre still, they can look just like 2D. But when they move, you can tell its CGI. Its probably because that they lack the imperfections 2D has which in my opinion is much needed and can be quite appealing. AI has the potential to rectify this issue.

Also any 3D animation that simply lowers its frame rate is not replicating how 2D animation works. They're just making their animation choppy. 2D animation almost never feels choppy despite it being "lower fps". 2D animation typically works on 2s. So for ever 2 frames, theres 1 image. This can change dynamically over a shot. So it can go from being on 2s, to being animated on 4s, to then in some rare instances, being animated on 1s. The youtube link I provided does exactly this. (Go through the video using the < > keys to see where they animate on 1s, 2s, and even 4s) To recreate this effect in 3D, you basically have to animate in the same process as if you were animating using 2D.

The most painful way of doing it, is animating at your standard 24 fps getting a nice result, and then just lowering it to 12 fps and creating a janky mess. Its a lazy practice with bad outcomes in a desperate attempt to make it have a hand drawn feel.