For CardGameDB specifically, I've tried the deckbuilder and I do not like it as much as NetrunnerDB's. NetrunnerDB has slightly more powerful filters that I can set by typing; a collections tab I can use if I'm building a limited collection deck; more compact lists of cards that require less scrolling; an influence display that I find clearer, especially when I have MWL cards in my deck; and a legality setting that can turn off the MWL for when I'm building onesies decks.
That's not to say that CardGameDB is without advantages. I can see that some people might prefer having filters that are simple to set and pictures of the cards that are shown constantly. But I'm not one of them. It's possible, I suppose, that this is partly because I'm more used to NetrunnerDB.
Without a deckbuilder that appeals to me, the forums there don't have much to draw me in. NetrunnerDB makes it pretty easy to post decklists here or on reddit, so the fact that it's a separate site doesn't bother me much.
I do miss all the discussion that is now on Slack. I am not good at Slack; I tend to dip in and out of discussions rather than spending all day following them. On a forum, I can catch up. On Slack, I can't.