I agree that RD, while effectively in most previous TW games, is most elegantly featured in TWS2. To think that all it takes to avoid the accusations of "broken AI" is a bit of narrative and a short FMV... I think ETW really missed an opportunity to do the same with e.g. a council of nations forming against you (as happened with Napoleon and the 1st French Empire), as you claim the inheritance of classical enlightenment as the "new Rome" (which every western nation did pretty much). MTW2 could have given you the same sort of thing -Holy Roman Emperor (a la charlemagne), Kalif or Basileus.

I admit that my game strategy in TWS2 hangs very much on exploiting pre-RD maximum expansion, then turtling to an acceptable point before sparking RD and launching my final conquest of the rest of the country. Nonetheless, dressing up the REAL total war moment makes much more sense to me and is a much more satisfying game experience, than apparently opaque AI behaviour.

I also think the RD is calibrated pretty well in S2. It hits at a good moment, when you are not supreme, and really makes you work for that supremacy.

In my curernt H/H Mori campaign I started RD with a warchest of 800,000 Koku. As Oda I'd thought 200,000 was overkill (from 80,000 as Chosokabe) but playing as mr money bags is fun.

Being a Christian Daimyo does make RD easier, particulary if you make extensive use of monks to incite rebelions in enemy provinces. Turning Christian does make the earlier game harder though (perhaps sparking a mini you-against-everyone period).