Main CQC Discord: 2,662 members
Major PVP Discords
Galactic Combat Initiative: 1,831 members
PvP League: 424 members
ECCE: 728 members
Major Powerplay Discords
Federal United Command: 1,390 members
ALD Discord: 1,161 members
Alliance of Independents: 883 members
...and some other powers, right? Can't be bothered to look them all up but they're probably not significantly bigger.
...and for comparisions, some actual big ones
Fleetcomm Exploration Discord: 12,863 members
General Elite Dangerous Community: 15,730 members
All very inexact, of course, but it's not giving me a "CQC is a minority interest, unlike PvP which is super popular" impression. (In practice Powerplay probably easily beats both, and, well...)
Main-ship duelling wouldn't work particularly well with the CQC format, since the high-end engineered ships probably wouldn't die once in the 7:30 allowed for a free-for-all deathmatch unless they got unlucky, and the scores in 15 minute TDM would also be pretty low. I'm not saying a simulated duel tool (with manual lobbies and matchmaking) to save you the trouble of trying to get everyone together in the same system wouldn't be a good thing - absolutely it would - but if Frontier were going to implement one, starting from CQC wouldn't really gain them very much.
I've been in the CQC discord for years, I can't remember the last time I checked it.
A lot of these ideas have been suggested time and again, it's just a matter of getting them to happen. The CQC format is great, the LOS radar and high-speed, twitch-accuracy requirements make it exciting. It just needs a little love.