Seriously - V12 also feels that way to me. Better in roundabouts but worse in simple speed control. Chuck Cook has talked about this too (or was that AI Driver ?).
In V12 I also have some lane selection issues that I didn't have in V11. It never seems to know when to change to the correct lane when a turn is upcoming. It can change to the left lane when right turn is just 100 ft away in rush traffic and then reroute causing 10 minute delays. Worse, when I've initiated the change at the right time manually - it tries to go back ! V11 had issues too - but not this much.
So, my overall disengagement rate hasn't improved much, even though I don't have to disengage at roundabouts as much as in V11.
BTW, on freeways V12 seems to be worse, even though many here think the code is still V11. Speed control is definitely different. V11 would just go to the set speed, if possible. With V12 I've had occasions when FSD sits next to a slow moving truck and refuses to speed up even when the lane is empty. So, basically FSD has decided the traffic is "moving slowly" because of that one truck and refuses to go faster. I never experienced this in V11 - so, surely the code is different in freeways too between V11 and V12.