[Machinist] What is going on?

[CKNovel]

But how does reducing the Chain Saw fall off help it in raid?

Criterion dungeon and ultimate, possibly add phase such as P3S.
Dancer and Bard are very strong in their own aoe game which makes them shine like crazy when there's two targets.
On top of that, their skills fires a straight line or damage around them, making them naturally cleave their surroundings.

MCH on the other hand is much more limited, Ricochet is locked on target and Bio blaster is barely worth on 2 targets.

It's only going to help MCH in certain content but it's exactly where it needs the most attention at the moment.