Rehzon makes some compelling points. Especially about the Mother Box healing Cable of that virus. Joe has used examples of the Mother Box healing Darkseid and Superman as reason enough that his Cable would be healed of that virus that limits his powers. What Joe has failed to realize is, the Mother Box only healed Darkseid and Superman's "physical" injuries. Darkseid was beaten by Doomsday, Superman's arm was broken. There is no proof a mother box can actually heal a virus, which is completely different than a physical injury.
Rehzon is onto something in his reasoning with the Mother Box as well and his other points.
My vote is for Rehzon.
It's unclear that the items Joe assigned to Meta-level Cable would actually turn him into Uber Cable. That was a gamble, and given Rehzon's evidence, I have my doubts about whether it would pay off or not.
Also, I've repeatedly objected to Magneto being drafted as a PM in the past, and although I gave up doing so as it happened so often, my view is that if you take Magneto at PM, then you don't get the benefit of his high-end showings, i.e. drawing on the magnetic fields of other planets, or tossing aircraft carriers around. And if Terrific uses his prep window to demagnetize his team's items, as I think he'd at least attempt to do (he'd be mad not to), then a PM-level "classic" Magneto would be significantly hampered in this environment.