There's a hidden advantage here apart from moving away from Microsoft, or having 1st party controller support.

Game devs will have a precise target to optimize for.

If enough steam machines and steam decks are out there, it simplifies porting software since you have a handful of fixed targets to hit. A studio could easily buy a few of these appliances for testing and development, and know for certain the product will run as intended. It's a luxury currently enjoyed by consoles, and it really does help their dominance in their respective niches.

This also helps smaller studios since the bare minimum means targeting a known steam platform, rather than pulling machine specs out of thin air and taking their best shot. It's a much easier problem to solve and takes a lot less time and money.

I think there will always be room for high-end gaming, but as long as you're "steam machine 2025 compatible" or whatever, you know what you're going to get.