BrawlVault is actually an extension of the KC-MM Forums, and I wouldn't consider BrawlVault dead, as people tend to make daily submissions. However, the same can't be said about the Forums themselves. I personally think that the Forums are in one of the worst states they've ever been in. While we're not constantly experiencing 503 errors anymore, the forums are barren and are filling with bot posts at an alarming rate, as there's no active Global Moderators to purge these bots. These forums are also in desperate need of an update, both visually and functionality, but there's only one website coder in the KC-MM staff, so this is easier said than done.
Though that doesn't mean KC-MM hasn't had a legacy built up throughout the years. You would be correct in saying that KC-MM was the go-to place back in the day, but with various big name modders either disappearing and/or retiring over the years, alongside Smash Wii U/3DS and Ultimate releasing, traffic to these Forums has been steadily decreasing up to this point. Despite this, I try to visit these Forums at least once a day.
If you want to keep in touch with Brawl modding, Discord is the way to go. Though I personally wouldn't recommend going to the KC-MM Discord. I would instead recommend going to the
Custom Brawl Modding Discord. Alternatively, if you want to know what specific users are making, then you can head over to the
Brawl Modding Workshop Discord (I'm not in this one, as I'm not active enough, but if you want to keep track of what I'm specifically doing, then I have
my own Discord, which is dedicated to my works).