This is correct, it is designed to fit loosely around the keycap mounts (of several manufacturer's mounts). If the pad fits too tightly on the mount then you end up pushing the pad into the switch on the down-stroke; i.e. pin-cushioning. Yea, they would be easier to install if they held onto the mount; it's a tradeoff that you have to accept for performance.
I'm afraid I don't understand any of that.
"If the pad fits too tightly on the mount then you end up pushing the pad into the switch on the down-stroke; i.e. pin-cushioning."
What, where, how? Do you mean that if the hole is too tight, the round cylinder in the keycap will catch on the edge of the hole in the pad? That's exactly why you should have a smaller hole in my opinion: keep the pad inside the keycap, eliminating that possibility entirely. The same hole size should work for all or most Cherry MX keycaps, I imagine.
"it's a tradeoff that you have to accept for performance"
In what way do you gain performance from having a loose pad under the keycap instead of a fixed pad inside the keycap?