The MR hate needs to stop.
Seriously.
The argument has logical faults all over, and if we did go back to UA as a spender they would have 2 choices.
1: UA keeps the same power, but in turn you fill with drain soul for 60% of the rotation.
2: They nerf ua, to keep the same soul shard generation, and a single cast of ua does around the same damage as a single cast of MR does now.
Option 1 is literally worse gameplay. I would NOT play a spec like that.
Option 2 you didn’t change anything. Why even bother.