SteamOS will most likely be deployed on other handheld PCs, not desktop PCs. The handheld PCs that came out in response to the deck's release (or before) usually run Windows.
Android is not bad because Android itself is bad (well... it kinda is but let's just assume it isn't), but because the phone manufacturers lock down their phones' hardware. They do this to force you into their ecosystem. With SteamOS, you already have an ecosystem, which is Steam. There is (at least for now) a clear distinction between Hardware manufacturer and software provider.
For now at least Androidization is nothing you should worry about. Maybe in 10, 20 years. edit: and even then it's never going to be as bad as with the smartphones
I agree that we shouldn't worry (at least for the moment), but I think the main reason is the lack of locks, both when it comes to hardware (no locked bootloader) and software (customizing the deck software is very easy, and if needed getting root access is trivial).
With SteamOS, you already have an ecosystem, which is Steam. There is (at least for now) a clear distinction between Hardware manufacturer and software provider.
Currently, the only officially sanctioned version of SteamOS is the one that is shipped with Steam Deck (even though it's bound to change soon), which is hardware sold by Valve (ie, the same company making the software). Meanwhile, most people using Android don't use Pixel / Nexus devices and thus their hardware is not being sold by Google.
So I'd say this depends entirely on how do the new manufacturers wanna go about it when it comes to offering their own custom versions of SteamOS. At the moment this is ok because Valve has been acting as a "benevolent dictator" and they have essentially had a monopoly on SteamOS 3 devices until now. Once that monopoly breaks (and if Valve actually allows third parties to ship their own customizations) we'll have to see what kind of control will their partners want to assert over it.
The thing we should be more concerned about are the parts that Steam haven't opened up, for example Steam input. However they've done everything as openly as possible for the move to Linux and I applaud that. If steam goes away or stops being so open, we still have proton and wine and other projects that mean we're not locked in to a Steam-specific OS, so we avoid the android problem there too.
I've been considering switching my deck to bazzite, tbh, because I prefer gnome so much, and I like being to use desktop mode when I'm out. I got a tiny Bluetooth mouse keyboard combo that looks like a remote or flat controller. I'm the only one who drives in my family, so I spend a lot of time just sitting in the car, waiting at doctors and stuff. It's nice being able to take just one device and work on school work or something.