EGS is perfectly usable and in my opinion is better than Steam in some aspects (way less bloat, open the app and your games are right there to launch even if you’re on the storefront), your saying they refuse to improve their product just shows you’re not using it because it’s way better than it was on release.
And yes, Valve has a monopoly, they control enough of the market that it goes where they decide it’s going and they’re the default solution people turn to when they need the services they offer, they’re also working on increasing their reach with streaming on the platform, forums, reviews and so on. If all you need is found on a single platform and it’s the platform that a vast majority is using then what do we call that? That’s right, a monopoly.
Want a similar example? Microsoft is considered to be in a monopolistic position with Windows, yet they have competitors, same with Office, same with Explorer back in the day. Google is a monopoly even though competitors exist.