Ok here is one from a user named Dio who just happens to write drivers for the R9700:
Notice the part where he says A lot is due to the adaptive algorithm
which sounds a lot like a speed optimization to me.
Next taken from the Extremtech AF article:
ATI's adaptive implementation of AF is a trade-off between not applying AF where it isn't needed (in ATI's opinion) and using dynamically more filter taps on affected areas, with the most severely affected areas getting the most taps. It's a kind of budgeting of AF that ATI believes delivers the best net effect.
ATI readily admits that its technique selectively applies AF, and makes no secret about not applying AF to the entire 3D scene – unless every surface is sloped relative to the view camera, an almost unheard of case. ATI engineers knowingly implemented AF in a sort of "triage" fashion, where the most severely affected areas get the most filtering, and unaffected areas get none (other than bilinear or trilinear).
However I dont have time to find the ATI engineer nor the PR speak that also says the same thing that they wanted to create a "performance mode of AF". When I have more time tonight I can try to find those if you still need to see em. But I think I have proved my point that the R9700 AF was designed to run this way for speed. Not due strictly to a budget of transistors. And thus is not "broken" in ATI's eyes.