@tatsu It would be easy enough to test. Just take a mapgen map, give it a new name (something catchy like "Winter Duel"), don't upload it to the vault (because that's against the rules), but host a custom 1v1 on it, call the lobby something like "all welcome."
Do that with 5 mapgen maps and 5 popular custom 1v1 maps, and see how long it takes to find people willing to play. I'll bet there's no real difference, in terms of how long it takes to find an opponent, between the mapgen maps and the handmade maps.
And we already know that about 85% of TMM people would rather play basically any mapgen map than play another 2v2 on Forbidden Pass.