Why the steam-deck should count as a console
The last traditional console where the game actually had full access to the hardware was the wii, when you ran a wii game it could use all the ram the system had, all the CPU power, all the GPU power.
This helped the wii against the much more powerful competing consoles, not enough to eliminate the gap obviously but if the wii also had to run an operating system while running games the situation would have been a lot worse.
Modern consoles instead have rather wasteful operating system that does eat up resources while games are played. The steam deck is probably a lot better than PS4, PS5, xbox one, xbox series X, etc in that regard in that it doesn't eat up nearly as much ram and doesn't reserve any cores specifically for the operating system.
Modern consoles are basically locked down PCs with operating systems optimized specifically for gaming. With the steam deck you at least have the option to install some other operating system if you want.
btw: sony originally allowed people to install linux on PS3 only to later update their system to block that.
Of course consoles should also have standardized hardware so it's easy for developers to specifically support said hardware and the steam deck does satisfy that since the different versions of the steam deck only differ in terms of storage and the screen.
While developers tend to not do much if anything to optimize games specifically for the steam deck one advantage you still get is precompiled shaders allowing you to more seamlessly install games to the hardware. Sharing pre-compiled shaders has been a feature of the Linux Steam client for ages. The Deck just benefits from all those users having the same hardware, so the hardware overlap is much greater than you'd expect from random user machines, and it's hardware that Valve definitely have access to.
The steam deck does try (and partly succeed) in delivering the good aspects of console gaming without the bad).
If console stops meaning (device with a super-restrictive OS preventing you from freely installing programs or installing a new OS that would be a step in the right direction.
btw: xbox consoles actually have a developer mode giving more freedoms but it's still rather restrictive and unpractical to use.
If this development continues we might see consoles evolving yet again
Type0: no operating system and allowing anyone to make a game for it.
Type1: No operating system but games needing approval of the console maker
Type
2: Having an operating system run only when no game is played. Games needing to be approved by the console maker.
Type
3: The console constantly runs a highly restrictive operating system but it also lets the user install some other operating system.
Type
4: The console constantly runs a restrictive operating system and does not allow the installment of some other operating system
Type5: The console runs an operating system giving people freedoms in addition to allowing people to install some other operating system.
Type
6: The console runs a semi-free operating system and does allow any other operating system to be installed.
What's common is that consoles are made specifically for gaming and have hardware and user-interface to facilitate that.
