One area of focus missing here is game streaming / remote play (Steam Link, Moonlight, etc. over a local network).

I've come to accept input lag, but mostly play games where it doesn't matter (simple platformers, turn-based games, etc). I know steam link from my home desktop to my ~5 year smart TV is adding latency to my inputs – though I can't tell if it's from my router, desktop, or TV – but I've come to accept it for the convenience of playing on the couch (usually with someone watching next to me).

I know some blame is on the TV, as often if I just hard-reset the worst of the lag spikes go away (clearly some background task is hogging CPU). And sometimes the sound system glitches and repeats the same tone until I reset that. Still worth putting up with for the couch.

Build an sffpc, have it by the tv :)