Yeah, you are right.
With one gone for "full fare", there are 3 left for different price points. If they anticipate high "volatility" or high price-spread, 3 steps are not much. In Y, lowest to highest bucket is at least 10x. But in Y+ fares most often must be squeezed in between typical Y and J pricing so the spread is likely less wide.

But I am not convinced LI/BA/VA is going to exist in Y+. I think 1 full-flex, 2 "flex" and 1 "saver".
Also, how can they differentiate in earnings?! If PR and BU-saver is kept there is not many meaningful earning slots in between. You can't really have a Y+ BA at 167% and a Y+ VA at 175% and a Y+ PR at 187% - to little difference to appeal.

So I think they need to a major shake-up in all fare- and earnings-structure in order to make this new cabin work.