^What makes you think I'm talking about human progress slowing down? Remember, the Klingons were initially more advanced than Earth, but by the 23rd century they're about equal. So clearly humanity was advancing faster than, err, Klingonity.
IIRC, humanity's rapid advancement is one of the reason's the Vulcans were putting up "roadblocks" in the 22nd Century. Of course, once the Coalition/Federation came into existence, humanity could draw on the technology of other members to keep pace with the Klingons,