I think the problem is that the only way to compete is with a hardcore, dedicated, and coordinated, premade team, or playing against terrible competition. In my experience with sub-max level pvp, there's 3 kinds of players.
1) Casual. They aren't particularly relevant, because even if they were coordinated, they wouldn't be able to do much, anyway.
2) Hardcore casual. This is where I would be. Players who do a reasonable job to twink their character's gear, but not being part of a dedicated pvp guild, lack the coordination to compete. I usually find enough similar players to make a difference, but most other hardcore casuals don't care about communication and coordination, so even if the effort is made, it usually falls on deaf ears.
3) Hardcore. The players who are dedicated to this bracket with their character for the foreseeable future. This seems really pointless to me, outside of max level. There's no rated matches, no significant reward, no stakes, imbalanced classes (impossible to avoid), and mostly a lack of significant competition. Sure, I want to play to win, but I don't want to stay in any low level bracket forever, nor do I want to commit to a guild just to have a decent shot at a single facet of the game.
Unfortunately, I don't see a way around this problem. You can't just ban communication between players, nor can you force players to make an effort to coordinate.