i also think that t6,t7,t9 and to a lesser degree t8 (AF) require some quick thinking. But alas its second coils, thus not available to everyone.
I also think that Yoshida said that the reception of rng and lack of telegraph skills on Stone Vigil HM got a nice reception; And that they are looking for a way to do more of this without punishing the party if one player can't follow (similar how you don't need a tank or healer for the second boss of Hullbreaker and if a party is good, for the last boss too)

Don't get me wrong, i think the game would do good with more random or semi-random elements that are not punishing too much, would make DR much more interesting then it is now, but i also think that its a fragile balance that needs a lot of time and experimentation to implement properly. With the last set of expert dungeons i think they are on a good path, and we need to give them more time for more of that to come. Especially since a lot of their manpower is focusing the expansion.

But please do remember that a person with a slight lag might die on Tam-Tara HM last boss if it doesn't have a reaction that can compensate for the lag. Similar is the last boss of Stone Vigil HM. Puzzle like bosses like second boss of Stone Vigil HM become even more boring after few times.

To me, and some other players, a fight isn't interesting if it doesn't require an effort, test of skill, reaction, awareness. But the threshold of what turns interesting into frustration is different for every player. Thus the same fight with different party members can turn from fun to anger. The balance is the key and that balance changes depending on the progress of the game (expert DR isn't the same as high lvl DR). Thats why some of us say that coil v2 and later, savage is an option when you clear all the previous content.

If you put too much rng components in a fight but they aren't punishing enough, people will just ignore them. With higher ilvl and echo that threat is even lesser, making people ignore whole mechanics (like the lass boss of Lost City of Amdapor Keep, where you can eat the first cast, tank lb second or if dps is good enough kill it before the second cast).

What am trying to say, you need to have all of this aspects in mind and how they reflect on the game and its population. Currently the RNG is "hidden" behind a ilvl and difficulty wall. The stuff that isn't even now gets ignored. Hard to balance the range of 30-40 ilvls (70-110) where the dps can go from 150-450 and tank hp from 5k to 10k.

Just try to remember/observe your reaction when you see a healer with 3k hp or a tank with <5k hp in Titan HM.