The flap wheels would have taken all day on blades that are very dull. I tried them and they didn’t work.
I have been reading up on grinding wheels getting glazed. The harder the wheel, the easier it is to glaze up. These are cheap wheels I am buying in bulk from online. I will try dressing them on a concrete block and see if that helps.My wheels are glazing up and becoming ineffective fairly quickly. When I put a fresh wheel on, at first it grinds really well and will dig in if you aren’t careful.