If it were really 8ms of added end-to-end latency compared to local, then it would be a complete non-issue – even in the twitchiest fighting games and shooters, unless you’re a literal pro-level player, as you mentioned. Most people would not be able to tell the difference even if they were specifically looking for it. It would even be tolerable for VR.
Unfortunately, the reality is more like 80-120ms, at least in one benchmark:
https://www.pcgamer.com/geforce-now-beats-stadia-in-our-inpu...
And again, that's not to say that they can't notice the difference or something, it's just not the dealbreaker that it seems to be for some vocal people. I can definitely tell the difference but it's not intolerable for me. I'm definitely happy to trade it for better convenience in many cases just like many are evidently happy to trade it for cheaper hardware.
Tactical shooters and MOBAs are still immensely popular despite the fact that most consumers likely experience a fairly high level of latency. People play games like Fortnite because they're fun, not because they're so competitive & fast paced that 8ms of latency makes a difference. Even competitive games nowadays try to soften the direct correlation between player skill and wins using matchmaking and RNG mechanics so everyone gets a reasonably consistent rate of winning. Want to play a really competitive and fast paced game where 8ms probably does matter? Play Quake Live against the 100 or so people that still tolerate that level of competition.