The opposite: they can actually use multiple cores more efficiently. All current GPU drivers are essentially single-threaded because of the limitations of OpenGL/DX11. If you look at something which really abuses the render queue, like X-Plane, you will see the all the rendering is done in a single thread because the overhead in syncing multiple render threads from multiple cores gets very messy very quickly. Additionally, Vulkan/Metal/DX12 allows you to do things like bake in GPU state changes so the CPU has to do zero work creating the next render state which will safe an enormous amount of overhead.
And play what exactly? Like I said, almost none of the big titles are on OS X. The ones I play the most—Project Cars, Mass Effect, Fallout 4 and GTA V—are all Windows-only.
1. Blizzard games - Starcraft, Warcraft, Diablo
2. Minecraft
3. Galaxy on Fire 2
4. Bioshock
5. DOTA 2
According to Steam, Portal 1 & 2{original and Lost Coast}, Counter-Strike, Left 4 Dead 1 & 2, Grand Theft Auto (series?), Half-Life [1, 2, Deathmatch, Blue Shift, Source, Episode 1], Call of Duty 2, Call of Duty Modern Warfare 2& 3, Borderlands 2, Dirt 3, Civilization IV, Batman Arkham Asylum, The Witcher 2, Metro [2033 Redux, Last Night Redux], Assassin’s Creed Brotherhood, Duke Nukem 3D Megatron Edition, Duke Nukem Forever, Trine 2, Grid 2, Deus Ex,. I don’t play any of those games, but I’m pretty sure most, if not all, of them are AAA titles. I pretty much just play StarCraft II, Minecraft and Galaxy on Fire 2.
Also, a number of Windows-only games can be played in OS X using WINE:
https://appdb.winehq.org