So I just upgraded my Mac mini's memory from 8GB to 32GB and I wouldn't expect to say this but this actually makes a HUUUUGE difference. I'm have an LG Ultrafine 5K hooked up to my Mac mini and while the graphics may still not be as smooth as on an iMac it's certainly a lot closer. The launchpad is smoother, mission control, the dock, swiping desktops, and pressing fullscreen. it's all gone up. It appears to me that MacOS isn't so much heavy on the GPU, but much more on the CPU and the memory. Funny that I'm coming to this only after 9 years of heavy Mac usage.