Drywall – Remove thick, painted joint compound from walls

My husband and I recently bought a home where a joint compound artist applied his trade :). All walls and ceilings are covered in those half-circle swirls and the ceilings go one step further to create concentric circles! Our home is 40 years old, so there are at least two coats of paint over this texture.

After requesting two estimates and not receiving a response after they came out, six weeks later we bought an electric drywall sander. We tried skim coating first – four applications later we've barely covered the texture. We own a business, so my husband has minimal time outside of weekends. I thought I could work the sander and he could skim coat on the weekends.

We have a space of about four feet between a window and a corner wall. I started with 120 grit and worked for about 20 minutes in a small area with no progress. I jumped to 80 grit, concentrated on one strip from window to corner for about five minutes applying a small amount of pressure to the sander with a minimal amount of progress. I realize it won't be completely smooth, hence skim coating. But I feel like I should have had better results.

Are my expectations too high? Is there a different method I should be applying before sanding? I'm ready to use a grinder on the wall!! By my calculations, it would take a day to just sand the room (not including the ceiling). Any tips would be most welcome – including a visual or to-the-touch idea of what the wall should look/feel like before starting to skim coat. As a side note: I did read the post at Best way to remove textured wall (joint compound)?, but the texture on the wall and ceiling is thicker than even that. I did suggest to hubs putting up new drywall and got a resounding "NO"!