The gamemode isn't inherently broken, but the way CTF maps need to be constructed violates so many of the fundamental design sensibilities of TF2 mapping that such a gentle map as landfall would never work.

This isn't to say it's not fun before people figure out where the camping spots and flag running routes are. It just doesn't have any of the properties that can let a map be enjoyable after the optimal flag running routes and camping spots are solidified.

Why was Vanguard added without the non-halloween version of Sunshine being made official? Not that 5CP is popular in pubs, but it'd be nice to have in there.

I suspected it might be because of vanilla sunshine's theme assets, but it's an outright guess

The thing is that the assets in all of 2015's community maps have been packed into the bsp files instead of being added to the game itself, meaning licensing assets should not be an issue.

it is most definitely still a licensing issue since they're still going to be distributing those assets. Different scale? Sure. Still an issue? Yes.