Not the OP. But I feel if we time DT markers to markers before this expansion they do not line up. Either the attack is going off faster or the marker is appearing later. I am not sure which, but the margin of error is less. That I am sure of. You have to watch visual ques more instead of reacting to markers. Except the camera is kind of unhelpful, some bosses flash text because camera can't see the visual needed. How is that good design if the camera can't show arms being raised.
Now with less time and people who need to concentrate more on rotation. The difficulty scales way harder for them. You probably don't even think of what skill to use next. Some players don't get that muscle memory. So keeping track of rotation and the new less forgiving markers. It should be easy to see how DT has been difficult for some.
The final issue and you might have seen a post about someone failing over and over with trusts. Trusts are bad for players that have trouble with the new markers. DPS gets one hit maybe two and then they die and they have to restart the fight from the beginning. If they would just be a little more social and get a group together their mistakes wouldn't be so punished.
Put of the problem is consistency. The game should have a hard rule for how markers appear. Not oh one you have to watch weapon and one look for the visual in the background. But oh this one you can follow the markers. Some systems can be unique. Some should not. I don't want to play any game where I have to guess how combat is going to work fight to fight.