I'm very passionate about the topic of the Steam Deck because of my Linux nerddom and following Proton since its inception, I love that there is an affordable mobile device out there that enables a seamless console-like experience while still allowing for tinkering and hobbyist ideas. I'm waiting on an eventual OLED model to purchase one. So I hate that the inherent coolness of this official Valve mini-PC is muddled with people console warring.
The incessant noise that Steam Deck makes the Switch "obsolete" because they're both portables is silly. To this day, I can't think of many devices that actually match the Switch's seamless hybrid functionality (e.g. swapping between mobile and desktop without a hitch, immediately swapping performance profiles and pairing wireless controllers without a fuss) except maybe the Analogue Pocket (?). There's the PSP video out, laptops with HDMI, Retroid Pocket, Ayn Odin and now Steam Deck that enable external displays but require further tinkering and don't feel as nice as the Switch's UX. The Deck has its own value by being a mini-PC which enables a host of modifications and access to a massive library of games.
Convenience is a general reason why people prefer consoles to PCs. It seems that people lack empathy surrounding this. I play PC games at 4K 60/120 Hz on an LG CX so I have tasted the fruit of bleeding edge high-fidelity gaming and it is glorious, but it is still inconvenient compared to just booting up a console and picking a game. Even if that inconvenience is a small amount, it makes a big difference over time.
Portability bolsters convenience, so it bugs me that if someone says "I'd like a Deck, but it's too large to consider carrying with me" that a common response is "oh but the Switch is unergonomic and is just as big with the Hori pad attached". Can't force a subjective experience onto others, I think the Switch's form factor is OK, and there are ways to improve the ergonomics without making it as big as the Deck e.g. grips, Switch Lite. So yes, Deck being a massive device is a fair reason to not want one if it is inconvenient or unaesthetic for the person using it. It not having an OLED display is a fair reason to not buy one, just as it is a fair reason to not get a Switch because one doesn't want to rebuy games.
Ultimately the Switch is doing gangbusters, it is a solid idea that will last and Nintendo are in a good position with future hardware by enabling DLSS. So I don't think it's worth taking any "Deck will eat Switch's lunch" comments seriously. I just wish the console warring rhetoric would end, and people would stop trying to force a perspective onto others.
(Ugh, I typed way too much but I've had these thoughts since Gabe Gear was announced... uh, apparently almost a year ago. Time to lie down)