From what I understand, Mendes had a strong vision for the show--some of which was toned down during previews--and Bernadette fit her performance to that vision. By many accounts, near the end of the run, Bernadette began to do "her own" Rose, which was noticeably different from the show that opened a year prior. Probably for the better. With Gypsy, much like King Lear or Hamlet, you build the production around the actor in the lead role, not the other way around. Laurents built a production around Patti. I don't know how thrilled Patti would have been to fit her performance into Mendes's production.