Apparently when I added support for scales for A_Custom3DRotate and many other parts of SRB2's code during 2.1 development (somewhere between 7-9 years ago), I failed to notice that I had mistakenly added scaling to both the angular speeds set by var2 for this action. This unfortunately means that scaling the actor up/down also scales the rotation speed, as katsy has pointed out to me through gifs recently.
Hopefully this action should work as intended for all scales now with this fix.