I think it's worth noting there's a difference between a toxic player and something bad being said to someone; people are just throwing it all in one basket.

A toxic player is someone who instigates an some kind of drama or negatively comments on another player needlessly. I just played as a BRD, got 4 kills, did 120k dmg and still lost. The DRG did 30% less than me, had no kills, was running around for no reason and wasn't backing off when the healer was dead. I bind and LB the healer who healed up with a CD as I popped my ranged LB, animation locked. He comments "lolbrd", "gj with the lb" etc. This is after he failed his own LB twice and died 3 times. He didn't let it go and carried on until he scurried away after seeing his results. He's still low Bronze, I'm halfway up Gold.

Everyone should be able to follow marks and know how to burst a target down by a reasonable amount. It's just a competitive environment and people just want to do well.