Actually, Miketz isn’t the rarest. I read somewhere that we read it an average of once every ten years. It has nothing to do with leap year.
I believe Kedoshim/Tazria are rarer. I’m not even sure if we ever read Haftaras Tazria.
FYI there is no such thing as Haftaras Va’yelech. If combined we do Netzavim, if separate, then it is Shabbos Shuva and we read Shuva.