if the steam deck doesn’t do the same I fear their sales will plummet until a new model comes out.

What will happen is the Deck will consistently have smoother gaming performance as developers optimize their games for the hardware, just like they do with consoles.

No sense in bothering with that for a piece of hardware that gets a new generation every year.

Also Valve probably doesn’t care if consumers choose a different handheld. Their goal was to create/expand a market to sell games, and they’ve already done that. Their work is basically done at this point. Same idea behind Steam Machines that were 100% developed by 3rd parties.