The coming of Bison was expected and even anticipated. What many were not expecting was that the character would come with a small balance patch that somewhat changes the game.
The Street Fighter 6 developers had earlier said that they would be doing more patches for the game, stepping away from their initial one-patch-per-year policy. They seem to have already started with the new DLC character also coming with some small changes to some characters.
The character most hit seems to be Zangief who had until now been looking quite top tier. His St. MK was nerfed and put back in its pre-season 2 state as they explained that it shifted the ground game too much in Gief's favor.