Our knobs are very tight on the unit and you should just have to pull to get them off. If they are stuck on with grease the only recommendation we have is to use a small pencil torch to warm up the shaft to loosen the grease.
Heck, I’d just like to congratulate Imperial for inventing metal knobs that don’t fall off after the heat of expansion/contraction loosens them up.
I know what you mean about getting some off though. The harsh and corrosive environment in some kitchens can ruin setscrews & such, or get in there around the D-stem and act like the knob is welded on.
I’m guessing setscrews aren’t the obstacle you’re dealing with. For some knobs, I’ve had to use a set of flat screwdrivers to pry at each side equally as a gear puller would. I’ve never ruined a valve by doing that. I HAVE had to destroy some plastic (mica) knobs for their not wanting to be removed.