You said there is no successful second app store

it isn’t widely used

So, it’s not successful, but it could be. So they were in fact correct that it’s not successful.

I use fdroid, so I know exactly how badly administered it is compared to Play. There are apps that haven’t gotten updated in months or years, despite the app on Play or Github being much newer. There are typo-squatting apps, and apps uploaded by people who do not own or manage those programs. It’s a wild west experience, and the average android phone user isn’t going to know enough to sort the wheat from the chaff.

Valve would be better off doing their own android offshoot OS.