I believe she being answer to dive meta is a really good thing.
But she being so powerful so much so to the point of dominating the meta is not healthy for the game.
On paper, you should be able to easily counter Brig by running Junkrat or Pharah then dealing splash damage while not directly engaging Brig. However it doesn’t work because Brig heals so much.
Currently Brigitte can heal as much as passive Lucio(without amp-up) and more than Zen when she combine her burst heal with her passive heal.
Brig avg heal is 6.9k Lucio average heal is 8.6k Zen avg heal is 6.8k. Considering most of Zen’s number comes from his ultimate, Brig provides far better sustained heal than Zen and almost-slightly less than that of Lucio source Overbuff
If you reduce duration of her passive heal from 5 seconds to 2.5 seconds, she can still activate her heal full time as long as she is hitting something every 2.5 seconds.
She will still be as effective as the same against dive meta because there is always something for her to hit.
However if enemy team decide to not confront her in close combat, she and her team will suffer from lack of heal as she can no longer provide so much heal.