The reason they added anti-healing as DPS passive was to mitigate the insane sustain characters were getting overall. However, with the addition of a new tank, supports now have an extra (and meaty) target to heal and an extra (and strong) enemy to deal with, and all that insane sustain some supports can provide is now not that much of a deal anymore.
Problem is this passives are insanely badly tought of because they don’t account for a simple fact: every character plays differently, and while characters like Kiriko, Baptiste and Ana have some sort of burst healing and/or immortality to make up for the passive, characters like Mercy and Lifeweaver suffer a lot to keep up.
In my opinion, Blizzard should consider rethinking the DPS passive for the 6v6 mode.