MCH only need a good buff on many of his potency.
The rotation is fun, gameplay is good, utility is always fine. -10% on boss and 30sec of 5% dmg taken is nothing to laugh at.

Beside the whole "let's buff potency" thing which by itself would be enough as long as handled properly.
One thing that must be changed is Rook Overdrive

The concept is actually very nice, you consumme your turret in a one big shot.
In practice, the damage they gave to the skill is currently too low.

Basically, using this skill and resummoning the turret assap result in a 15sec without a turret.
So beside a few cherry pick situation like Susano rocks or Lakshmi bubbleadds, there is no situation where you wanna loose 15sec of turret.
A good start would be to buff the skill damage so that using it does not mean DPS loss NOR gain.
It just convert the next 30sec of dmg into a big shot.

Doing so would make it a much more interesting skill as it would basically be an on demand huge burst and MCH-DPS would not be penalized for using it on priority target. At the same time, we do not want that skill to do more damage than what the turret would do in 30sec otherwise it would be another "use on CD" skill.
And I do believe the beauty of this skill is to be a situational skill that you use when you need it only. Not whenever it's up.