Alright, I'll tell you what, I'll go through the spreadsheet in the OP and let you know which features I think are a net negative and why (this is going to take awhile):
Chat - The chat implementation is poor and the my gaming experience would be better without the "community" overlay. It would be better to have no chat at all or have an implementation like Battle.net where it's a seperate thing entirely. Either way I'll still use Discord because it's the better way to chat.
Curation - This is a big one for me, the lack of curation makes browsing the store page a bad experience
Curators - Trying to replace their curation with "community" curators just clutters up the store pages with recommendations from people that I don't want to see
Early Access - Whew lad, what a shitshow this turned out to be
Marketplace - An avenue for money laundering, market manipulation, and an incentive for devs to implement shitty "drop" systems
Achievements - More distractions from popups
Community Guides - The community is garbage
Community Discussion - See above
Trading Cards - Something that could have been cool but instead turned into a reason for people to idle in games for extra cash, more distractions from popups
User Reviews - Community is garbage redux
Inventory Support - How is this a feature when it's necessary for their broken marketplace? Moreover, the inventory system is ALWAYS broken in one way or another
Anti-Cheat - Can be bad depending on how the Devs and/or pubs implement
MTX Support - Can be bad depending on the game as well
Leaderboard Support - Rampant cheating (despite "anti-cheat") make this a net negative
3rd Party Keys - Just a vector for key resellers to profit off regional pricing
DRM for Devs - Boooooooooooo
Now, these are my subjective reasons for using Steam less over the years. They may not match up with your feelings on these individual features and that's fine. I have other reasons, listed above in other posts, and likely more that I'm not thinking of right now.
You shouldn't be loyal to a storefront because of momentum. Over the years Steam has become bloated with unnecessary features that, in my opinion, makes playing and buying games on the platform more of a chore than is necessary. Small annoyances and inconveniences are all that is needed for me to want to take my time elsewhere because, luckily, there are other platforms that offer storefronts.
They'd go a long way to winning my time and money back simply by curating content and policing their community, but I understand that Steam doesn't NEED my time or money, they got plenty from other people.
And to be fair to you, I'm going to go through each of these points:
Chat: No it's not the absolute greatest thing in the world, but it's more than serviceable after the overhaul. And it's optional for the most part. I really don't think it's hurting anyone's experience that much. Like seriously, it's not that intrusive. I literally just checked to be sure.
Curation: Can't really argue with this one. There are people who want curation and people who don't; it's simply a difference in view.
Curators: This ties in with curation.
Early Access: eh... it has its good and bad. Mostly bad... so you get this one.
Community Guides/Discussion: Sorry, but this is lazy reasoning on your part. "Community is garbage, therefore useless." No. There are tons of helpful guides and discussions either for technical issues (what I use it for the most) or gameplay strategies and whatnot. To hand-wave all of that as "garbage" is, as I said, lazy. There's usefulness there whether you like it or not.
User reviews: Ties in with the above. Now obviously there has been abuse of the system for sure, but overall, I still think it gives you a decent barometer of how games are, especially smaller ones where you can't really find much information elsewhere.
Achievements: They are 100% optional. There is literally no reason to complain about them. Turn off the notifications and never worry about them again if they bother you so much.
Marketplace: Again, optional. Money laundering? itaintthatserious.gif Again, you can ignore the drops by turning off notifications. Can't speak about the market manipulation. Can you give examples here?
Trading cards: Yet again, optional. Admittedly, they were way better in the beginning. Now, they're just kind of... there. But again, they can be easily ignored. They're not "hurting" anyone's experience if they don't want to use them.
Leaderboards: Can't speak on them because I don't really use them. Is the supposed cheating any worse than any other platform?
Anti-Cheat/VAC: Come on, you're going to have to do better than that. "Could be potentially bad maybe depending on things" is terrible reasoning. And that's not even unique to VAC; you could say the same thing about anyone else's cheat system.
MTX Support: Just like with the anti-cheat system, this "potential" issue is not unique to Steam. This sounds like a general complaint related to all microtransactions.
3rd party keys: So? It still gives users options to buy outside of Steam while remaining in the ecosystem. Remember, devs can also generate their own keys too and sell them on their own.
DRM for devs: not really sure what your issue is here? Are you saying giving the option to devs to implement DRM is a bad thing? If so, that's not unique to Steam. Every other client outside of GoG and itch.io allows that too. Devs can do DRM-free if they wish on Steam, just fyi.
So yeah, you do have some valid points, especially on the curation part, but most of your complaints are either not unique to Steam (cheat system, drm, etc) or pretty trivial (you're really gonna complain about 100% optional, completely ignorable achievements? come on). Plus you ignore all of the objectively (or subjectively objective) great features that have both improved Steam and PC gaming in general, like the controller API, expanded Linux/MacOS support, Steam Workshop, and others.
Again, I feel like many of your complaints would be solved with a little configuration on your end.