It's not really a failure.
Linux distribution and diverse ecosystem brings a level of complexity.
The only way to support it long term is to either having your team continuously update and release builds of the game to cater for that which is an impossible task to ask for a lot of studios.
The initial approach of runtimes did help but it's still has its limitation.
If now a studio just need to test their game under a runtime+proton the same way they would test a version of Windows to ensure it's working under Linux it's a win/win situation. Proton becomes the abstraction of the complex and diverse ecosystem of Linux which is both its strength and weakness.
Another solution would have been everybody using the exact same distribution which would have been way worse in my opinion.
And who knows, maybe one day Proton/Wine would be the Windows userland reference and Windows would just be an implementation of it :D