Just cause it has the theoretical power doesn't mean anything.
Macs are not build for games in mind and it makes them subpar (to say the least) in this category to anything on the windows side ESPECIALLY in same price range. Every grandma and their dog knows this.
I completely disagree that Macs are not build with games in mind. Apple put a very competent low-power GPU in the base Macs that can hold its own to entry level gaming PCs in optimized games. Apple also offers state of the art APIs and tools for game development.
The problem is that there are not many developers who know the platform, and not many studios that target Macs. But this is a cultural issue, not a technical one. The thing about culture is that it is known to change. As some few pioneer studios decide to invest their time into a high-quality Mac version (like Larian does), interest in Mac gaming will increase and we will get more games. The biggest roadblock - weak performance and buggy drivers - have been cleared. We will see in a couple of years if Apples gambit plays out.