I think you're focused too much on latency, in theory stadia should be REALLY good on that for games that are coded well. In theory, since a lot of it is hard to quantify. In the optimal scenario the stadia user boxes all talk to each other at near zero latency and do little to no error checking or server handshakes since they live in a firewalled space that users cannot hack. So you've eliminated a shit load of latency that every console/PC player already has. Second the controllers talk directly to stadia boxes instead of going through a middle man (PC, console, phone) which eliminates even more latency and separates any latency into controller latency (input) and visual latency (display, output).
For fighting games and shooters it could end up, again in theory, BETTER than pc and console since you've cut out a lot of stuff in the middle that adds lots of latency. To online games, of course local/LAN games will always be better.
Unfortunately i doubt bungie or anyone else is doing any of the work to completely optimize this and it doesn't not seem like Google is giving any fucks about ensuring the absolute best way of playing every game is realized, given that they aren't even letting people use the controller wirelessly with other devices yet. Also since every game is seperating user pools by platform it's gonna be interesting to hear how many players are even there, Destiny 2 should be fine since every stadia founder gets it free but how many people are really gonna pay $60 (again?) for MK11 or RDR 2 to play online?
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