Is the computer in question really "more than capable" if it "can't play the games [you] want to play"?

I've used geforce now on my mac before and didn't have latency issues. I wasn't using it for any competitive games where you need ultrafast twitchy response, but I did use if for plenty of FPSes and never had any issues. And I don't have super fast internet, just the basic package from Spectrum. So I wouldn't say it's bad, though admittedly it might not be the best latency achievable in the gaming world.

i wouldnt go as far to say "its horrible".

i would never recommend it to someone who otherwise has a capable computer, of course, but it really isnt that bad. i gave it a pretty thorough test out of curiosity, and when they sponsored a few streamers i watch, it was totally fine. with the caveat that you have a decent internet connection and its probably not good for twitchy games like counter strike.

and, as far as i know, there is limited support for modding and some unsupported workarounds.

I used Shadow PC for a long time. Never any issues over several years. Lots of reasons in preferred it over GeForce. I can expound on that later if needed