I really don't mind when games switch to 30fps for cinematics, I'm currently playing KH III and it doesn't bother me at all.
But I also never for a second thought "wow, thank god these cutscenes are 30fps, it looks so much better!". What does make a difference is the wonderful per object motion blur kicking in, but it would look either just as good or better at 60fps, given they adjust the shutter speed accordingly.
Real time cinematics with proper motion blur and good direction/camera work will always look even better when the refresh rate matches the gameplay, in my opinion.
I do agree with people who said that more temporal resolution means flaws can be more apparent, but wonderful animations can also be highlighted even more. In this case, shouldn't the issue be shit tier animations and wonky camera work, instead of the temporal resolution making it more evident? Ideally, we'd want our games to have better animation and cutscene direction, not to get better at hiding how shit they are.
Or at least that's how I feel as someone who thinks that animation quality is the most important aspect in making a game look good. "The game is beautiful but the animations are bad" is something I can't say about many games at all. Poor animation work almost always ruins a game's graphics to me.