Yep, I noticed the same. It looks like Stadia version is set on medium detail. The same with RDR 2 that seems very blurry comparing to pc version. Which is surprising considering the hardware Stadia relies on.
@davetenay The fact here is that the hardware doesn't matter if the port doesn't make use of it, as @DaBaldEagul suggested if you see how Cyberpunk 2077 runs there is no reason why older games run worst than that. The truth here is that developer responsible for porting games are still getting used to the architecture, think about PlayStation lifecycle, each generation first games was much lower in quality than latest games for the same reason, more time passes more time the developer have to better understand the boundary of the platform (and with Stadia we can only go better with time!)