In the brush editor there is an option in the bottom “eraser switch size” if you enable that checkbox. Krita will remember the size of the brush in erase mode. You just have to increase the size once.
I’m the same as you. I usually want a larger eraser than the brush I’m using. There are already good answers here – here’s another option. You can assign a large eraser to one of the “10 brush” slots in the python plugin.
Unfortunately Krita doesn’t natively support a decoupled eraser and probably never will. This is annoying for painters who also use other programs. For now the Buli Brush Switch plugin is the best workaround for you. A bit fiddly to set up but the closest to what you are used to.