Sweet and spot-on with what I've experienced. Finishing-up with the floor stripper (ZEP product from HD) shouldn't take much effort based on how much I've alreday removed. Yes, chalky looking surface once stripped and agree with not wanting to remove anymore gel coat and re-apply, maybe a re-finish job down the road.I dealt with similar on my old boat. The floor stripper was the key - used a garden sprayer and worked in sections. I also found that once the floor stripper was visibly working, i could clear a lot of it with a power washer.
The stubborn spots I hit with a green scrub pad. You can get a kit on Amazon that puts those on the end of a powerdrill, that made life much easier.
I don't know about hitting it with sandpaper, as I think it would really gum up the paper very quickly, especially if you have many coats of it.
If i recall correctly, poly-glow is basically the same as mop-n-glow, which is why the floor stripper works.
If it's like my old boat and they applied it properly, the resulting finish after you strip will be pretty dull. Then you have to decide to either re-apply or try to compound and wax back to a shine. My attitude was that I didn't want to remove any more gel coat, so I carefully reapplied. It actually looks pretty nice if you put it on carefully.