Stadia was released in 2019, while Proton came out in Alpha in mid-2018. It's highly unlikely it was available to Google when they started developing Stadia.

Furthermore, controlling the full platform has enormous advantages in terms of scalability, low-latency streaming and control.

and enormous disadvantages. Like costing hundreds of millions of dollars to build, and on top of that, spending hundreds of millions in payouts to studios to port their games.

The hubris to go ahead with something like this....

If it had worked, it would have massively paid off for everyone (Google and studios alike). Studios already have to develop special versions for the different consoles and PCs, what's one more? Google just needed to keep at it, invest more money (it's not like they don't have billions laying around) to bring studios in, and send strong signals they're serious (like promising to refund everyone in case of shutdown).

> so making it worse in this fashion doesn't achieve any particular goal that I can see.

I can see at least three goals it achieves:

1. It helped to establish the superiority of Google engineering (in the minds of Google engineers), e.g. "We can do it better because we're Google."

2. It helped somebody (or multiple somebodies) in Google get promoted.

3. It signaled to the market that even as a new entry into the gaming market that Google has a big stick to wield and publishers/developers will have to bend to their will, and /will/ do it.

Was Proton viable back when Stadia was built?