The biggest thing is that Brigitte is the first hybrid tank/support that we’ve released. That alone has the potential to create entirely new comps or counter existing comps.
Specifically for Brigitte though, she also can be very difficult to rush down and quickly kill. She can be very defensive with her shield and high health/armor, but she also can shield bash any enemies that come too close and knock them away or potentially just kill them. Players have already discovered how scary she can be to fight against as a Tracer player, as an example.
I’m not sure she will completely upset the dive meta just by herself, but she should certainly help!