I’m really not. Your argument only works where steam is selling exclusive content, they are not. You can run steam on other devices along side a bunch of other app stores so it’s not a captive market at all.I think you're missing the whole point of the Deck. As mentioned above, Valve sells software, not hardware. Developers adore a consistent hardware spec to target (just look at watch the Switch can do after 8 years) and this is probably the first popular mass-produced fully-fledged PC hardware standard we've seen. In a way "Steam Deck Verified" is much more important to Valve than 60Hz in AAA titles, and it's important to game developers as it's a captive market ready to buy the next title that appears with a "Verified" tag.
I understand that PC gamers are used to yearly refreshes and constant shiny trinket to buy. The deck isn't that, and there are loads of other options if you want that. The Deck is a vehicle to sell Steam Software. The bits they will want to address and improve are battery capacity, runtime and to a lesser extent, cost.
If you can get a better/different device than a steam deck to run your steam software or worse, other games stores/launchers, valve will be losing sales to other hardware and harming its install base. Like it or not, devices like the Ally are real competitors and they will not be the last. Dell demo'd a ‘deck’ device before the steam deck actually launched. I’d be surprised is there wasn’t an MSI and Gigabyte handhelds in the next year.
The desks USP was/is the price. However, they are not currently selling the two cheaper tiers which puts it much closer in price to it’s competition.
The switch is a closed platform and it’s the only platform to play Nintendo games and it’s Nintendo games that sell consoles not the rest of the library (mainly trash) on the store, it’s a very different proposition to the deck.