As I stated, it is cumulative, so it doesn't really matter if the brush is soft or hard edged. It's just time and repetition. There's nothing inherently wrong with the functionality of selections and the like - within Photoshop as such. It's just the way it works. At this point, I'd like to know exactly what you're trying to do ie: a technique, effect or a finished product... and don't be shy. I'm sure it's something we can all work out.

Regards, Wayne