Ahriman
Tyrant
You are correct, the Mahdi Zealot has an iPower of 0.
It seems like there are a lot of bugs here, potentially. As you say, this is probably from a missionary unit being the core, and the Sardaukar one is probably from a copy paste from the senior one to create the junior one.
Seems like this parameter needs a general audit. This would explain a lot of the very strange AI power ratings.