They suffer from uneven or inconsistent input-to-display latency. If Stadia can give everyone the same, (hopefully) modest amount of latency, the games remain as fair as they ever were
I'm not entirely sure, but you may have misunderstood my point. It's not about fairness, it's about whether it is physically possible to play the game on the same level of skill.
Talking about shooters, in the traditional multiplayer setup input-to-display latency isn't actually a concern, because input-to-display doesn't go over the network at all. When you move your mouse, the display update loop doesn't contain a network roundtrip. There is only the concern of latency to the server for resolving which hits actually connect, and I agree with you that having this latency be roughly the same for everybody is probably quite a bit more important than how low it is.
With game streaming, the input-to-display loop does include a network roundtrip, which makes it harder to aim.
If you've ever tried to play a shooter with <15 fps, or suffered from the mouse input lag that some games used to have on Linux in the past, you should know what I mean: aiming with the mouse crucially relies on a feedback loop where you correct your hand movement based on what you see on the screen. The longer that feedback loop takes, the harder it is to aim.
That's what the concern is with competitive shooter play on game streaming services. (And it's why I wrote that other types of competitive games may not be affected as much, but it's been a long time since I've played a lot of games, so what do I know...)
I don't think so - the reason I don't use VSync for first person shooters is because it introduces 1 frame (8ms ~ 16ms depending on your frame rate) of input lag. It really feels laggy when I try to move my mouse and aim.
And mechanical keyboards make you type faster and gamer glasses make you aim better and a tincture of molybdenum in your star-water will cure your cold
