My opinion of Breakneck has shifted pretty dramatically with the last few games - introducing a bunch of crap that the map was never in a million years designed for breaks the entire thing.
The Banshee's balance issues are well-documented, but on the Headlong variant, it has a hard counter with the Gauss Hog's inclusion. Breakneck has no such counter. Rockets are useless since they can't lock onto a maneuvering Banshee, and they don't fly fast enough to hit anyway. The sniper and DMR have a hard time hitting the thing when it's flipping all over the place in a confined space with a lot of floating objects as cover, and the Plasma Launcher's anti-air capabilities are a big joke.
Headlong has always had a bit of sniper dominance. With the mancannon on Breakneck, the offensive team has essentially just two safe routes outside the base, either going through the invis hallway or using the single Warthog (the lack of decent vehicle transport is another problem). The old Valhalla problem (yes, it was a problem) of being crossmap sniped when you have no control over your movement in the air, as well as camo campers at the landing zone basically renders that route off-limits, which in turn limits how many ways you can get into the base. Teleporters aren't ideal, I get that. But neither is limiting the viable routes for an offensive team by virtue of cheesy play.
Then there's the (probably biggest) problem that armor abilities simply weren't a twinkle in the designers' minds when Headlong was created. The map is based on distinct elevations and routes up to higher levels, a concept destroyed by the jetpack. Getting grenaded from a jetpacker who jumped from ground level to the back tunnel of the red base is infuriating because the map just wasn't designed to have cover for that sort of scenario. As mentioned before, camo guys will just lounge around at the lift landing zones with the shotgun relatively unassailable. Of course, evade does its usual thing. There was a very distinct pace to asymmetric objectives on Headlong, and that's something that is completely lost with Breakneck. It becomes a jetpackfest with no sense of flow and just a bunch of sloppy play.
The most unfortunate part of this is that Headlong, far and away the better version of the map, almost never shows up with 1 Flag or Bomb. It's always Breakneck.
On a related note, I had the worst game of BTB in terms of randoms in that playlist so far tonight on Breakneck.