If Sombra (who is supposed to fill the DPS role for the team) Cannot secure kills, takes way too long to engage and open up the choke for a push or defend a choke, is more away from the team then helping the fight, Is that her fault or the teams?
Her entire hero design is supposed to be this solo assassin hero and if she gets a good hack off, her team can follow up on it (Eg: Rein, Bastion, Hog, Any other tank really) as she can solo the other dps without their mobility in a solo situation however, Sombra's damage output just can't outdamage what she has to go up against.
The toxicity is drawn from the fact that Sombra cannot SECURE the kill and the team is upset that there is nothing coming from the dps and the other dps can't really work with Sombra at all because Sombra's entire purpose is to go work alone by her self, leaving the team at a 5v6.
She cannot protect the supports at all in anyway as her damage is not enough to out damage whatever is targetting the supports down.
The problem with Sombra will always be her style of play as of right now is more solo reliant then ever. And on ladder, Most sombra players will be running around with the mentality to hack whatever they see first, to gain some advantage out of it, translocate away, heal up, then fight again while trying to ensure they are not found in the process.
If a Sombra is spotted, she's one of the easiest characters to focus down because of the fact that one's shes being focused on, her abilities and damage can only do so much for her.
Do you see the issue now with Sombra? So when people are toxic with Sombra, its not necessarily toxic to the player, more over, that Sombra as a standalone hero cannot do enough for the team on ladder unless in a pre-made group.
The same situation applies to Bastion. Unless the team plays around that hero very very very consistently will the pick work. Same with Torb as well.
Its better to have something consistent rather then cost the team the entire match.
I'm not throwing shade or insulting Sombra players, this is my observation as my best friend plays support and Sombra and this here is somethings he has said from his time in Masters and above.
-Shrug.-