Way back when I ran sysprof and friends on linux, I think something like 20-40% of the system load disappeared in to the aether and some of it could be found in pieces that sent off draw calls to the Intel driver. This is on a Cinnamon environment where the GPU is being used to composite windows and do some minor effects, but many applications are still CPU rendering as-needed.
Now keep in mind on macOS you are sharing that same intel driver not with one or two light loads, but all draw calls on every window are being routed through Quartz or similar. It makes most of the UI slick and pretty but there is a lot more contention for draw calls on the mac. (It’s the same user story as the filesystem; file handles on macOS are more expensive than Linux, but they’re also being heavily hooked to run Spotlight and Time Machine indexing.)
Tertiary, Apple doesn’t like OpenGL. They stopped maintaining it some time ago, and its officially deprecated these days. So you’re fighting other apps for the same chip and you’re doing it through an API thats driver is sabotaged/undermaintained.