I will be doubling back on normal this week, but my experience does not match yours.
For instance, your description of Ursoc doesn't fit mine. Why would you be using tranq
during Focused Gaze? You would be using it on the recovery period after taking Trampling damage, which occurs at the end of the charge. It is very easy to tranq without moving during this recovery period.... Similarly, if the raid needed topping off
before Focus goes out, I saw no issues. Additionally, the damage from Cacophony is significant on its own to make Tranq useful. I personally will have to see more of Mythic before deciding what areas are truly the most dangerous, but regardless, I never was never very concerned with movement during Tranq.
I have similar opinions for your other fights, you are just throwing our "general concerns" with those, but every fight in every tier has those and I have always worked around them. Yes, Xavius is not a mana concern, so good point on the PoTA leading traits not mattering there. Dragons is the one fight that truly concerns me (I have already said that).
Anyway, I am still contemplating the decision
It is a very transient one anyway.