We could also argue that Vulcan's thin air is the very thing that makes Spock strong. His entire respiratory and circulatory systems are designed to "compensate" for that, that is, thrive on Vulcan - so when he gets a higher partial pressure of oxygen, he gets a bit giddy (but hides it well), but his muscles can now sustain exhaustive activity for considerably longer than human muscles, thanks to the extra oxidizer inflow. The inherently lesser-capacity copper-based circulation is simply "overengineered" suitably to produce this result.
Do Vulcans lose their edge over aliens when on Vulcan? It's difficult to tell from "Amok Time" where all sorts of weird factors are at play. But I remember people complaining about Vulcan lack of fighting prowess in those ENT episodes taking place on Vulcan, and this might be part of the explanation.