You can add non-steam games to steam if thats what you mean. Theres a launcher called hydra which does, things. Playnite is a launcher I use that I plug all my other accounts in to and launch all games thru that. There are also ways to unlock dlc and stuff but that will require a little bit of research. Havent sailed the seas for games in a while.
TLDR; Yes you can add otherwise aquired games to steam. For the most part
Retention for 90%+ of providers is at least 4500 days for binary files and 110000 days for newsgroups. Have two providers, one monthly and one block, that run on different backbones with one that takes down for dmca and one that doesn't and you'll be fine. There are very very very few shows or movies that you can't get. Don't have to worry about VPN, ratios, trackers or any of that other crap.
Don't you think app developers should have the freedom of choice for app stores? Android has multiple places to get apps, lots of FOSS apps aren't on play store, and likely aren't on iOS at all. Having the option for 3rd party store gives not just users, but developers too, an option and access to more apps/users that wouldn't otherwise be available. You want safe secure apps, that's all good.
You mentioned that an app might move away from the app store to a 3rd party store, if you already use and trust that developer's product how will having to get it from a different location change that?
Now, not to sound too harsh, but why your convenience of not having to go get another store more important than a devs ability to host their product in a different location?
I wonder if it has to do with the age of the player. I grew up playing old games, not first gen games but on commadore and such, ms-dos games. Win 3.1, SNES, etc. Graphics in games have never really meant much, sure pretty is pretty but I'm more than happy to play around with noita for a couple hours, simple art styles, blocky textures. I am also fine jumping in to cyberpunk or mgs or last of us or anything newer. As long as I find the gameplay fun that is first and foremost the most important part. IDGAF about multiplayer, to me multiplayer was a cop-out in the late 90s early 00s to not have to actually make decent games, and I still stand by that. IDGAF about stupid features. You make a game I find interesting and I'll likely play it, You make a game that looks pretty and has shitty gameplay I won't even spit in its general direction.