I wish Krita would simply default to an eraser preset when you first use the pen eraser. It’s not intuitive and not mentioned in the docs. I thought pen eraser support was just broken.
Yes makes sense to map eraser to the alternate pen tip. I’ll check if this is already requested. If not may be we can file a feature request bug report.
This actually should be happening already. What might be happening is that the store-last-preset-mechanism doesn’t quite work, and yours is always restoring some other brush.
The previous presets mechanism doesn’t work correctly. They seem to be stored correctly, as far as I could see from looking in kritarc. However, they are not recovered correctly on restart for the alternate stylus tip.
I did mention this in a bug report some time ago somewhere but I can’t remember where or when.
EDIT:Add: I didn’t raise a bug report for that, I commented on another bug report about the use of an eraser with the alternate tip.
I think the principle is that krita doesn’t have an eraser tool and so the ‘eraser tip’ of a stylus is used as an ‘alternate tip’, for which you can assign any brush preset. It may be that some people use this to quickly swap between two favourite brush presets.
If this was changed to make the alternate tip default to using an eraser, which eraser brush preset should be chosen? There are three default possibilities and some people may have created their own ‘ideal’ eraser.
It’s probably better to fix the previous preset store/restore mechanism so that everybody gets what they want and what they expect.