I agree with most of what you said but not this part. Its a weird thing in MMOs that people just don't do things because doing it is fun. They have to get some kind of reward or they won't bother. I don't like any kind of reward system in pvp because the reward should be pvping. If it isn't rewarding the game is broken.
The irony is that Tera has by far one of the best action combat systems in any game of this type, but the combination of ELO, bragging rights, gear disparity and the reward systems mean that 3s is never going to get an influx of new players. At best you'll get a slow trickle as players no longer need to be driven by incentives like gearing up. There are so many reasons not to play 3s. Protecting your ELO rating, grinding credits for better gear etc.
Competition naturally develops over time if a game is active and has healthy reward systems and player match making. So later on when you have a healthy scene, you can bring in ratings and bragging rights and prize money. but if you introduce these things too soon with the wrong incentives at play, it can really break a game.
Going back to Counter-Strike before the leagues and clanbase and all that, there was a game that lots of people played because it was fun and fair. You didn't care about losing, you weren't doing it to get something else. You wanted to play just 1 more match because it was really fun (after playing for 2 hours straight).
But theres nothing really fun about waiting 30 minutes in queue to get wrecked by a team thats 300 average rating above you and has better gear. The goal is to get more people hooked on the game, not turn them away from it.
The first time I played 3v3 was like 4 seasons ago and we were all in newly minted Conjunct. Literally the only players who were queuing during EU primetime and morning/weekends were Overpower teams because Overpower and feeders were the only teams we ever played in that season. So we got wrecked by Bluepoo and friends because they had better gear and more experience and we wiped afkers every other match. The experience has been off putting, even though some of the best times I've had in Tera were in the arena.