Eh it feels like the first phase goes for way too long when it's hard to actually screw it up- at least with 10 and 12 you're into a phase change in like 3 seconds, and there's a modicum of actually paying attention as dps, something that doesn't really happen in 11 till the add phase.
Maybe it's just tank perspective, as that is basically how most fights go, it's easy/boring early on and then suddenly you have to do things. And if you mess up at that point the group will probably wipe.
One very simple mistake in 11 can kill 2-4 people. Our group rarely recovers from mistakes in 11. 12 is typically salvageable because the penalty for a small mistake typically means the boss gets an additional stack, as opposed to half the raid dying.
I'm not saying it's a hard turn. I'm saying it's annoying to wipe to. T7 wasn't hard either but it broke up raid groups.
12 is probably most recoverable, I have seen some ridiculously crazy clears in there. But like if you mess up on charge/tethers in 10 or about a billion things in 13 you can wipe extremely fast over a small mistake, and then have to sit through easy phases again to get to where you were. T9 and T13 were actually the worst with this, since the fights are all stupid long and the first phases are extremely simple compared to the stuff at the end.
I'm not saying it's easy either, just that most coil fights have a similar gimmick in which one mistake = bad news. Second coil in general broke up groups because of this, seemed like every turn another group exploded. That entire tier was basically insta-wipe mechanics after insta-wipe mechanics.