I'm told the transition from S1 to S2 is not nearly as pronounced with the 12's vs the 10's. Someone even told me that was a badge change only just to avoid confusing the customer base and it's the same cab, but that needs to be confirmed/verified.
I would also say the transition is REALLY cab dependent. IMHO, the 410 is the special case where the move to S2 was beneficial. The 310, and especially the 210, IMHO, are designed such that the extra mid grunt is very helpful... just "over the top" with the 410. So at least in those cases, I think it was a negative move. I don't have a 210, but I can say I do prefer the S1 310 over the S2. However, I prefer the S2 410 over the S1 (for the same reasons you say above).
Also, just for another datapoint, at least in the case of the 310 (since I had one of each for a while) the mid bump in the S1 over the S2 was right around 380-400Hz. If I bumped that freq on a parametric using the S2, they sounded very close, except the S2 still had a little more going on in the high end (treble, not mids).
The S1 410 mid bump does seem a little higher to me, but not much, and I haven't done the parametric test to try and figure it out.