The effect on monks is almost twice as large as the effect on fighters.
You are trying to weaken PCs. You weaken them by X.
As a side effect, you weaken monks by 1.75X.
If the 0.75X extra effect is a "minor statistical swing", then so was the original X. The point is the unintended consequence (making monks weaker) is almost as large as your intended consequence.
Maybe someone else will think about that idea when doing game modification: that you should try to make the intended consequences of your changes to games be much larger than the unintended consequences. And you should examine the unintended consequences and not discard them because your original choice wasn't based off numbers, but your gut.
You can do insane things to D&D type games, and as the game is mostly about sitting around and bullshitting, nothing really breaks. That is why lots of stupid rules keep working.