AMD WHQL drivers used to be released every month and also beta drivers between that. Never had problems with AMD drivers and updated drivers for big games usually get released at the same time.
There is not much Nvidia can really kick up a fuss about for mantle, AMD is driving things forward, AMD are open to nVidia using it for there cards. But now because of mantle we see Microsoft taking notice and now adding similar options into DX12 so that they don't get left behind.
nVidia advancements are all proprietary limited to only nVidia users which segment the market. Open source is the way forward to benefit everyone which is why AMD for example backs OpenCL and nvidia goes with proprietary CUDA.
You are right that we need them both to keep up competition otherwise nVidia would still be selling titans for £1000.
I've had both Nvidia and AMD cards in the past but I now mainly try to stick to AMD due to Nvidias underhand business practices and being a bunch of cunts. Free feel to look into the nvidia bumpgate scandal, assassins creed DX10.1 removal, Batman Anti-Aliasing scandal, Nivida bribing Origin PC to drop AMD and bad mouth them etc etc
Nvidia are happy to lie, cheat and bribe anyone, even there own customers and partners.
The way you're meant to be played