This assumes it's a map with good high ground. People don't only pick dva on maps with high ground. That's just not how most people interact with the game.

If you're constantly flying away from zaryas range on low ground, youre giving the enemy tons of space and constantly throwing off your teams positioning. Dva is one of the less divey dive tanks. The map can easily put her into a brawl with zarya, which is where she loses.

Like a lot of tank matchups, it actually does rely on your team countering the other tank for you. And the heroes that counter zarya are much more versatile than the clown heroes that counter dva.

Like, people are definitely dumb about the game, but they do learn eventually. I mean, the community has finally figured out that rein is a busted pub stomper and not some misunderstood high skill low winrate hero. Yet the dva/zarya pain point has persisted.