Yeah, looking at this list, there are multiple things that could cause worse outcomes in practice.

The most problematic IMHO are the I/O prio and niceness. This is because other processes like xorg and the compositor (and maybe even kernel threads, though not sure if you can starve those) need I/O and CPU too when running a game, and they get starved by the game hogging these resources. I remember when running the original StarCraft through wine you needed to de-nice it to avoid starving the X server of CPU.

Of course some of the other stuff is also sketchy since it could increase temps and therefore induce throttling. Depends on how good the cooling is I suppose.

A low latency scheduler can increase overhead and thus reduce average fps, but should not really increase stuttering (probably the opposite), so I don't think that's the problem really.