https://www.metv.com/stories/mike-farrell-was-terrified-when-he-first-took-his-role-on-m-a-s-h

When Farrell joined the cast of M*A*S*H, the pressure was high, but the show's ratings proved higher.

In the 1974/75 season Mash finished at No.5 in the ratings. In 75/76 it finished at No.12. So there was a period of adjustment. Viewers didn't fall in love with BJ and Potter right away. Things improved the next season.