??? You just casually overlooking triple tank and quad tank meta long before Brigitte was released? Also some pro players and coaches were theorycrafting that a 0 dps meta would probably be the best and that too was before Brigitte.
It just wasn’t tried before because in pro play trying a dramatically different team composition is risky. They don’t just pick up different heroes to try things out, no. Every player has to grind and grind said heroes to get good enough and then the teams train together and scrim again and again to learn synergy and strategies. If it doesn’t work it’s a huge loss and almost guarantees you end up at the bottom. That’s one of the reasons metas are born. They aren’t necessarily the best team comps in existence but they are tried and true to work extremely well, they are trained to near perfection and if you mirror(where possible) your enemies you are guaranteeing you aren’t failing because the team comp didn’t work.
It literally also rewards tank/support players by giving fast queues every time they want to play some dps.
You have this weird obsession where evil bad people play dps and tank & support players are pure godlike figures who would never touch a dps hero.
Pro play has revolved around tanks and supports in almost every single meta other than maybe double sniper.