That’s getting after it. As 66vairguy stated previously, a wire wheel works well. Looks like you’re using perhaps a grinding disc or a flap-disc. I use typically a coarse wire wheel. Mostly a flat one, but sometimes a cone wheel depending on the area if it’s hard to reach. Makes a ton of rust dust. Then shop-vac out the dust.
If you use a coarse wire wheel, use with caution as wires will break off and become flying projectiles. A couple of years back, I had a wire stick in my leg. I was wearing shorts. It completely buried itself in my skin. I tried to dig it out but couldn’t. I gave it time to work its way out, but after 6 months it still hadn’t. I had to have it surgically removed. It was about an inch long.
As for the rusted out hole in the floor, hopefully the rest of the floor is solid. What’s your plan for the repair?