Interesting find! Depending on what issue that was, it was written by either Joe Gill (co-creator of Peacemaker) or Denny O'Neil (legendary Batman writer).
My thought has been that you get at-will powers, that can be boosted by expending a slot. Each at-will has a list of the effects that you can use by expending a certain level slot. No worrying about what spells are on your list.
Despite its issues, I still have a soft spot for Maztica. It was at least trying to do something different in the fantasy space, and it sparked memories of The Mysterious Cities of Gold for me. I still think Eagle and Jaguar warriors, and Pluma and Hishna artisans are very evocative class ideas.
Yeah, looks like they;re committed to doing a Psi-mage. I'll still down vote the spell related stuff at survey time, because I'm not going to lie and say 💩 doesn't stink.