But seriously, I have no doubt that some players are just so enthralled with Dominion that they put up with the nitpicking, the endless meta-discussion, and the board's unhealthy obsession with becoming a "good player". That is much more a testament to how good Dominion is than how welcoming the board is to people who do not conform.
If you don't want to become a good player, there are plenty of discussion boards online where you can discuss Dominion without getting better at it, such as reddit and BGG.
Man, I'm disappointed that you didn't include f.ds in that list. Like, there was the thread about Dominion memes. There was a thread about Card Alchemy where people were just doing wacky wordplay. These were all in Dominion General, which, you know, sounds like the place to talk about general things. (This is in Dominion general too FWIW.)
To be blunt, this is the point where I be that guy, and say that f.ds is not just what you think it should be, it is the amalgam of what everyone who posts there think it should be. Consider this as a signal of "your point is noted but I disagree that f.ds should only be for people who are trying to get better at Dominion."
Sure, the Dominion subreddit has a lot of Dominion storage posts, but looking at the front page right now, it has
a thread about what to do on boards with no trashing,
a thread asking how long it takes to get good at the game, the weekly Kingdom of the Week, and if you scroll down a bit there's
a thread asking about whether Goons is as ridiculous as it feels like it is.
The way I see it, you go to f.ds for the memes and to read articles comparing engines to phase diagrams. You go to Reddit to read about the Nth storage solution and people asking what expansion to buy. You go to Discord to play Pokedominion and to make fun of Seprix. As for actual Dominion strategy advice, you do that wherever you want to - there are enough good players overlapping all of them that you're sure to get somebody to tell you something reasonable. (Well, except for BGG - last I checked, it was too inactive for people to bother visiting there much.)
I feel the primary thing is that Dominion was super big before and is less big now because several people have moved on. Sure, people still watch for new expansions, but unless told otherwise, I would assume that the number of players has been holding steady or slightly dropping over time. (Where # of players is including people who only play IRL, but we need sales figures for that, and I assume they can't be publicized.) There's just less to talk about for the enfranchised people. That's why there's always a big burst of activity when new expansions drop - suddenly there's a big pile of stuff that everybody wants to talk about.
An expansion is coming out at some point, and I got to play with the cards a few times, and oh man, they're pretty neat and Dominion is still a pretty cool game. I feel like that's the most important thing.