What you've got to think of is that AMD aim to produce cheaper products on the market and considering this, they still produce amazing stuff. A thing for you to think about is that say AMD weren't around to compete with nvidia prices then nvidia has free reign to overprice thir products to a big amount compared to now and unless we were willing to boycott their products, which you cant if you plan on building a pc with a graphics card, then i wouldn't complain. If you prefer nvidea then switch no-ones stopping you and im just hugely thankful for AMD and I love all their products. (especially thyat r9 295x2, they're not afraid to break trends... Watercooling on a reference card .)
p.s mantle was huge for BF4 which is one the most popular pc franchises at the moment and youve got to givee it time for more products to include mantle support for the fact thats its still, generally, taking its first steps.