Apologies if I'm talking out of turn, I want to do my best to be a good ally but I recognize that I've got some serious blind spots!
With that caveat in mind, I would suggest that the problem making fedi unwelcoming is two-pronged:
1 ) It looks to me that fedi inherited the original sin of microblogging, which is that the system naturally rewards the spiciest hot takes that go with the local social currents.
2 ) Fedi's culture was established by FOSS geeks rebelling against for-profit social media.
This has led to most instances becoming machines for manufacturing hot takes are going to have an unacceptably high mayonnaise content, highlighting the importance of your points 1 and 2! Nerds have to learn to slow down and think before shooting their mouth off, but it's so tough to cut through the weird high school grievance politics.
(That mindset is a big part of what generated the whole problematic LessWrong/Techfash wave; your post fits in nicely with awful.system's core mission!)
My impression is that Twitter avoided this because it was initially colonized by a more representative cross-section of society. This can be somewhat remediated via your points 3 and 4, but will face resistance -- which kind of kills the fun of using fediverse for so many of the fedi-curious. This is a big problem when people can just go to bsky or whatever and find much of their old Twitter network already setting up shop and reconnecting with their communities.
Thankfully, some individual instances (like awful!) seem to get it, but for the most part the poison is already baked in, and it's hard to unbake a cake and begin again. It will also be tough to get the existing core fedi community to understand that no level of "technical excellence" can fix what is fundamentally a social issue. Unlike baseball ghosts, actual people are under no obligation to come just because you built it!
Other than the kind of long, tough reckoning that society as a whole needs to face, it's tough to see an answer. Do you think it would be possible to somehow begin and again have a "second genesis" of fedi, now that the wider world is more invested in finding alternatives to "big social?"
Thanks for working on this!