Ultimate Hat change was a terrible idea
Nobody complained about Ultimate Hat. People like it.
I like Nimbus Cloak, but you didn't need to remove Ultimate Hat to make room for it.
It is a terrible addition to the domination tree because you put it on one of the most important tiers for domination. Most people are not going to want to give up healing or movement speed for marginal ultimate CDR reduction, especially when it needs kills to stack.
By making it require kills you've gated most champions from being able to use it effectively.
Assassins aren't happier with this change because they were happy taking movement speed and then picking up ultimate hat from their secondary.
Mages, supports, and other ultimate dependent champions are unlikely to ever use ultimate hat now. Most don't want domination as a secondary tree if they can't benefit from anything else in the last tier. It's not a very appealing tree to non-fighters/assassins. Maybe only a very small amount of champions actually could potentially like this change, like snowballing fighters who go domination/precision and don't care about out of combat movement speed but rely on their ultimate more than in-combat healing. But generally this change screws over at least five times more champions than it benefits.
i as enjoying take healing + hat but yah
running around with a 1-minute cooldown on my ult without giving up MFB.