AMD cards were much faster than the Kepler equivalents, but now NVIDIA fixed their mistakes in that architecture and they are as fast as AMD cards. So AMDs hardware is good, it is just a software issue.
Was Kepler actually slow, or did it just seem that way because the 680 was built with their mid-range chip while the big high-end GPGPU-oriented chip was initially reserved for the server products?
Tesla GPUs are also rather slow, but the value of Tesla lies in increased double performance, larger memory and memory correction -- and you cannot beat Tesla GPUs in these departments.