Edit: Changed title as this is really more about the lack of incentives to build teams that were removed with free tourneys than leaderboard addition. Although I think that leaderboards are still a factor in toxicity.
The funnest this game has ever been was with free tourneys. The reason for this was you could queue with any number of people and placed in a match. If your team one you progressed to round 2. Won that? Your team goes to round 3. Then that was it. However many games you won, the better reward you got. The point was to win but if someone was a weak link on your team and you lost it wasn't that big of a deal, I could queue again or queue with friends to avoid that. Ideally this would have grown to have old GW1 style where you stay with your team till you lose. That created some awesome comraderie. Still, that's how I found my first PvP buddy's/team. We did great in a free tourney and then eventually stuck together to try paid tourneys.
Now, it's a mess. I queue up, solo or duo. Wait 6 minutes. And have WAY more to lose than if I win. If I win now I get slightly better reward track progression and some rank points. If I lose, I get slightly less rewards but ALSO I lose 2-3 wins worth of rank points on the leaderboard. This just breeds animosity, someone makes a mistake now is way more frustrating because there is so much more to lose. I can't form new bonds and stay with players I thought did decent, because I saw them in 1 game. That's not enough time to form a strong enough impulse to want to queue with someone when weighed against the risk of losing 2-3 games worth of rank points. Not only that, but if i am duo'd we can't queue with that person.
We can't have fun with new builds because it alienates teammates who also have more to lose now than back then. We can't form new bonds with people because the risk is too high. All we can do is queue with who we think are good and slowly grow to hate everyone else. And play builds we know are good.
In free tourney days, I had a desire for other people to get better because I might have to be with them for 3 games in a row.
Now, I just hope that person isn't on my team.
What we have now is not a formula for a healthy community the way free tourneys were. ATs were kind of a growth from this but also fail to breed comraderie. I don't want to risk playing with people I don't know because of the time investment of an AT. I don't want to waste an hour standing around to not win the whole AT. I want to do two ATs a month as to not waste my time. If we lose... I'm already mad at my team because now I have to do at least ANOTHER AT and waste at least another hour to get enough QPs.
TL;DR: leaderboards Make it so there is too much to lose now for little gain. Max duo queue means no way to form new bonds anymore. [Edit: Free tourneys incentivized teams and allowed them to spam games together and not have to wait ages for ATs]. There is little reason to try new things besides to counter meta now because it just triggers teammates. This combo is a complete 180 from the community of free tourney days And it's leading to a toxic community.