You aren't going to be able to make support attractive enough that it has pick parity with the rest of the roles without making the game subjectively worse for everyone but supports. Players don't like to be denied and would rather kill or be killed trying than just deny someone else a kill.
I agree it's probably not possible to hit parity, but if we can improve the proportion even a little, it will help with queue times and not having to use autofill as much.