@FoxlukeITA : More than likely it is just due to the deployment of this new title. It could be that they are still trying to fix some issues in the deployment across all the Stadia servers and data centers and for this reason you are seeing this issue but on other games you are not.
Unfortunately, you may just need to give it a bit of time for everything to get stable and run more smoothly, I suspect that it is still very much a little bit of a learning curve for Google with the behavior of these games when running on Stadia, and at the same time having an evolving platform too.
If you don't see any drastic improvement within the course of the day you could contact support and see if they can recommend anything, of course if you have played more than 2 hours of the game then a one-click refund is out of the window, but that doesn't mean to say you couldn't discuss the matter with support and still get a refund.
Or, the other alternative is just to wait it out and check to see when the performance has returned to an acceptable level. That is pretty much the case that I had to do with Trials Rising where it played great, then degraded to a very laggy/jittery experience, to now a great play once more, that took a few days to get rectified though, so I hope it is quicker for you.
I have the same issue only while playing on my MacBook Pro over wifi. I only get 'Good' connection even though I'm 12 feet from the router with no walls in between. Moving closer does not help. Same wifi (5GHz) gets 120 Mbps. However, on CCU with ethernet it's flawless. Something with my wifi config.