You could get a more powerful desktop PC (It is very easy to build a PC these days, children can do it.) for the price most likely but as an entry level “console like” device the Steam Deck is absolutely astounding and worth picking up if the portable nature and simple software call to you. The biggest downside is that since it relies primarily on Linux and has a non standard control scheme (as in, a controller) for a computer you won’t get the full multifaceted desktop experience.
Regardless of that you will be able to run the vast majority of desktop games and it’ll be a great experience, it really is a wonderful piece of hardware with great software.
Steam is simply a marketplace on an open platform, there are plenty of ““exclusives”” between launchers but it’s rarely as a result of deals, more that Steam is the de facto PC storefront and as a result gets almost every game.
Mind, even if it is a little bit more troublesome to navigate maybe, the Steam Deck is still a full fledged PC. You can load any OS you want onto it and install any software you feel like, SteamOS/Linux just happen to be what is installed by default and the most custom tailored and user friendly experience but the sky is the limit with such an open device.
This is like buying a bookcase at Walmart and being torn up that all you got was a box with a bunch of pieces of wood.
Valve provided a value option for people who are technically savvy and wanted to upgrade the device themselves for cheaper, it’s not their fault you’re doing it wrong lmfao.