[Zord Commander]

You would have still needed a yellow that was female. And Kat was a built in replacement for Kim. Even with Five Shotgun Zords they still needed a second female with Zeo. If Karen Ashley didn't leave too, then maybe you would have a case.

But there is no way you could have had Billy as a male yellow. Since the Sentai Footage clearly showed yellow as a female. Unlike with Zyuranger, MMPR could have gone with either gender for yellow.