The Vulkan vs DirectX thing isn’t an absolute in terms of performance. In addition, it’s worth keeping in mind that Windows is horrifically bloated with unoptimized “features” and can use up to 8GB of RAM at idle plus 10-50% of your CPU at idle depending on your configuration as well as which unnecessary services are bugged in that update. That in and of itself makes a huge difference; my W10 install was using 8GB of RAM and nearly 80% of my CPU on system services for almost a month straight before they finally fixed the bug and reduced it to 2-4 GB + maybe 15-25% depending on the day, meaning I was getting huge stutter playing games as simple as Old School RuneScape. My Tumbleweed install on my much worse specs-wise laptop, on the other hand, used effectively zero CPU and less than 1GB of RAM at idle (fairly confident on the RAM thing but I’d have to check for exact numbers).

Having played Halo CE for PC recently…no, it doesn’t have split screen at all. That was only on the Xbox version (which is technically superior in quite a few ways). The only way to have split screen on Halo CE on PC is via console commands/mods. That said, I do agree with your overall point and I would love to be able to do split screen MCC on my PC without mods.