I like Rodgers, and I have nothing against McCarthy. That said, I think this is an interesting thought. Essentially, McCarthy will presumably let the starting QB play within his means. With Rodgers this means a more complex offense, more throwing vs runs, etc. This is capable of being successful based on last year. With Flynn this would probably mean a simpler offense with shorter routes, outlet receivers, more running, etc.
If this ends up being more successful I don't think it is a reflection of either the coach or Rodgers because, IMO the Packers' lack of success early this year is more a result of failed
execution by players other than Rodgers. I'm not saying he's perfect but there have been a lot of drops, missed blocks, penalties, etc. If it is more successful I think it will be because by boiling the offense down to the basics it will make the players concentrate more on the fundamentals - you know, catch the ball that hits your hands.
On the other hand, if the change is wildly successful and Rodgers comes back the following week I would hope that McCarthy would not revert back 100%.