Why does battle high exist?
The mechanic seems to serve almost strictly to benefit the teams that are already performing well and in a typical match for me it ends up just snowballing to a point where they become nigh-unstoppable and the game may as well be won already. It also makes playing with people who don't know when to fold and back out of a bad situation to avoid feeding the opposing teams kills all the more punishing.
Your only hope of actually fighting back against it is to viciously focus fire them down (With LBs if necessary) but in a group of randoms people are generally too disorganized to do this, especially if there are multiple players with battle high present.
Gameplay mechanics tend to benefit the underdogs if anything so the inclusion of this is honestly a little baffling to me and it's probably my biggest frustration with frontlines in general. Though there are a lot of other things that are keeping me from finding PvP very enjoyable; the second probably being the tug of war scoring system that both deducts and adds points for kills which makes bad/dumb players and bots an even bigger liability to have on your team and also drags out games.
Why is PvP so bad in DF? Will it ever improve?
I don't really get PvP in Duty Finder or Roulette. Usually there is no communication, coordination, or strategy of any kind. Everyone usually just splits up quickly and then runs around randomly, ignoring the objectives, fighting pointlessly, and dying. On our data center, Maelstrom seems slightly more coordinated, but I don't really know why that should be. Flames seem to avoid any strategy and ignore objectives usually, but I don't really know why that should be either.
The random selection of jobs doesn't seem to help; I've seen games where there is a single healer for the entire alliance.
Battle high may make things worse; it seems to make it easier for one team to steamroll another. But the root problem seems to be that PvP is usually just stupid and pointless, and there doesn't seem to be any system to help teams work together effectively, or to help players who want to learn how to play PvP learn to do so, or to help people improve, etc..
It's annoying and frustrating and really not much fun. I don't really see it improving either, as it was just as bad in ARR, Heavensward, and Stormblood.