It’s no secret that OSX isn’t really the right platform for performant games. Yes, I can play some games quite happily but there are limits. When it comes to UE4, playing as standalone does perform better than PIE but it does depend what you’re making. A simple game can run at 60fps quite happily but as soon as you throw in some complex shaders and dynamic lighting, the FPS drops quick.
In the case of the editor though, you’re experiencing further slow downs simply because of the refresh of multiple panels (which I’m sure has a CPU cost as well as GPU). In a stand-alone game, you’re only really refersing the game but in the editor, your refreshing the game, and the various editor panels.