The title is sort of misleading. Stadia Founder's Edition is $129 for 2 three month subscriptions (one for a friend I guess?), a Stadia controller, and a Chromecast Ultra.
Stadia Pro, what they're calling their subscription model, is $10/month which is independent of everything else and all you technically need to play games on Stadia using your Chrome browser, phone, etc.
Considering Steam is full of people who will notice the latency of something like this, I doubt Steam is worried at all.
I'm no MLG tryhard, but I notice the latency when playing my Xbox One X across my local 1Gb network. I wouldn't want to have that be my daily experience.