I agree with pretty much everything you said. Note that genies can choose to stay with their master after the 3 wishes and they still have powers, thought somewhat reduced. Jeanie has already expressed the desire to remain with her “master” Neil, so I suspect she still has to comply with his expressed wishes (certainly with leeway) and in this strip Neil asked her to return him to normal. Since Jeanie is thinking about finding out how Neil was better in bed than Jean, she didn’t bother to think of a “creative” fulfilment of that wish and it suited her agenda of the moment to make Neil male again.