No. They really don't. I've given solid reasons why this puts the high end casters to an even greater height of power, you've given no rebuttal. You just keep saying "no" instead of using logic. Either defend your position or admit you cannot.
Yes, they do. Almost no PrC gives a T1 something it couldn't already do in some way. All their additions are insignificant in the greater scale of things. And I don't really care about a few overpowered exceptions (like Rainbow Servant for example).