We understand your concern, but DX is holding back the industry from making the games they want to.
As others have said, Dx is actually what allowed the great advantages of PC gaming. The most appealing part of PC gaming to me is the ability to play current games, future games, and past games and not worry whether my hardware and OS will be compatible, as well as to play very different types of games. There is no current game that I have played, and I have a relatively low end system, in which I have said "this game sucks because it does not have enough units on the screen, or the image quality is too low." Would more be nice, of course, but there is a price to pay for that in compatibility. If I could not play it because of the lack of an appropriate API for my hardware, *that* would suck.
So both Dx, and supposedly mantle when we actually see the numbers, have advantages and disadvantages. It still remains to be seen how it all shakes out, but to try to paint Dx as holding back gaming is only looking at part of the equation. It may be holding back image quality, but it does offer forwards, backwards, and across hardware compatibility, which has made PC gaming the platform that it is.