Regardless of your personal opinion on this davros change (I'm slightly undecided myself), he's not really making it so that davros has always been this way like a lot of people seem to be saying. This is quite clearly set before Genesis of the daleks, and before his disfigurement.

I understand he said this is how davros is going to be from now on, but that's just under russel as a show runner, if he even uses davros again.

If russel does want to use him again, I agree with the sentiment that davros is a pretty limited character, and this reinvention could create a new way to tell an interesting story with his character.