8GHz below what it is supposed to be (macs tend to do that a lot). this isn't spectacular by any means and is actually well below what Dolphin recommends and very few users have listed chips of that grade as working and all of those were at stock clock speeds not.
If you are using a 2014 macbook air you likely have a down-clocked dual core i5 4250U chip and 4gb or ram using onboard intel 5000 graphics. This inefficiency can lead to some emulators requiring much much more powerful hardware than the original console did. This is why most emulators have problems even on very high end hardware and in some cases having too high end hardware can actually break games by making them run too fast for their engine. The gamecube is built to run gamecube games and the Mac is built to run x86 applications in a Linux environment.
First off comparing the raw power of your macbook to the original console isn't a valid comparison.
