Isn't Metal more powerful though, like a 4070 running on Metal would be more powerful than a 4080 on Direct3D?No because Apple doesn't use Direct3D or even OpenGL/Vulkan, they use their own Metal API and games not only need to run in x86 emulation they also need to translate Direct3D or OpenGL/Vulkan calls to Metal
The largest barrier isn't even the x86 emulation, that was solved long ago by Rosetta 2 and customizations Apple made to the Apple Silicon hardware. The largest barrier is translating to Metal, if you think this is easy then you have no idea how much of a pain in the ass it has been to make Steam Deck's Proton translation layer that translates Direct3D calls to OpenGL/Vulkan in Linux, even today there are many games Steam Deck simply doesn't work with and there is still a significant performance penalty for the translation