My experience with destiny on stadia is not great at the moment. It feels sluggish at best and it's really hard to play (I don't own any other games)
When I'm trying to play any of the game modes I am experiencing a lot of input lag and frame issues.
So far I have tried disabling hardware acceleration, mouse locking, forcing the better codec, turned off mouse acceleration, turning graphics options down, setting chrome as high priority with net limiter and through task manager, turning off all extensions/plugins.
I have a beefy connection (FTTC 400 down, 40 up, 7ms ping). Connected via cat 6 Ethernet.
My PC is also beefy (not that it matters)
I am not running any other programs and nothing else is using my internet connection.
I have the same problem! I tried all the fixes as you as well, and still cannot get it particularly stable, whatever game I play, including Destiny 2. Other game streaming services I've tried, Nvidia Geforce Now and Playkey, work beautifully on my laptop, which isn't particularly powerful.
I play with a gamepad, and have noticed that moving around slowly in a game seems to mitigate it, but if I make quick movements the gameplay starts to stutter and Stadia tells me my connections is "fair".
I spent some time chatting with Google Stadia's customer support, followed all his suggestions and still could not get stable performance. Very frustrating!