I'm a little torn reading this debate. On the one hand my own preferences tend towards ChipBoundary's; I can't ever see myself buying a Deck because I can't see myself wanting to play games in any situation that doesn't better suit a desktop or a (plugged in) laptop.
On the other hand, the Deck does have advantages, notably cost efficiency, the compact package, the built-in controls, the battery life, etc. The product clearly has merit, even if it isn't for me.
But more than anything I'm grateful that the Deck exists. Its wild popularity has improved software compatibility on Linux immeasurably--mostly in the gaming space, of course, but the story won't end there. Thanks to the Deck, more people than ever are aware of and interested in just generally making things work in the (non-commercial) Linux user space.
I imagine the Deck will have benefits for PC gaming more generally, too. First, it's just a new market niche for PC games; I'm sure most people who bought a Deck were already invested in PC gaming, but not all of them were. Second, the Deck adds an extra hefty incentive for game developers to innovate on lower end hardware, which can't just be dismissed as old or low rent, anymore.
With all of the crazy developments we've seen recently in e.g. the GPU market, and all of the pessimistic predictions flying around, the Steam Deck is a rare bright spot. It reminds us that, contra forum doomsayers here and elsewhere, PC gaming will not die any time soon, nor will it become the sole domain of fat cats.