My family was Mac-exclusive for as long as I could remember. However, I remember going to a family friend's house when I was little, and the eldest son had custom-built rigs that ran demos and full games that blew my mind. None of which (other than Blizzard games) ran on Mac OS 9.
There was a golden age of Macintosh gaming, especially in the edutainment sphere, Pangea Soft classics like Power Pete (Mighty Mike) and Bugdom, and older HyperCard stuff. (There are abandonware sites that can help you experience and enjoy old titles, but I won't link to virtualization tools nor the sites because they are in a legal gray area). It wasn't a "hard-core gamer's" cornucopia, but instead a niche market that mirrored the whimsy of the hardware on which it ran.
The modern age Mac gaming has left much to be desired, but with each iteration of hardware, Apple tried to emphasize that games of PC origin could run great on the OS:
MacBook Pro delivers both powerful graphics performance and long battery life. Every MacBook Pro features the NVIDIA GeForce 9400M integrated graphics processor, which provides an outstanding everyday graphics experience with up to a 5x performance boost. Power your way through the latest 3D games — including Call of Duty and Quake...
Despite this lip-service, it's always been to the contrary. Drivers for GPUs are managed by Apple and lag far behind the current versions provided by the manufacturers. Open GL versions languish behind every other OS.
The situation has gotten worse in recent years. Apple introduced its own graphics API, Metal, for iOS, and has since rolled it into OS X. The Open GL versions in OS X continue to lag (a decade!!!!) behind everyone else. After more than 20 years of providing excellent Mac compatibility, Blizzard snubbed the macOS with Overwatch and continue to point at Apple as the reason why it hasn't been feasible. Blizzard even attempted to port Heroes of the Storm to Metal and had an experimental toggle to enable the engine, but the performance wasn't up to snuff so they pulled it..
Hardware-wise, the Mac has never been a high performance powerhouse, never using desktop-grade GPUs on anything but the Mac Pro, but Apple could have tried to make life better for game developers. The deprecation of OpenGL is likely going to spell the end of triple A titles getting ported to the Mac.
Metal may be great for iOS, but it is harmful to make it the only show in town on the Mac. I couldn't be more pessimistic about the situation, which is why I urge Mac users to give up hope that Apple will reconsider their direction.