Martian Manhunter isn't skilled as astral plane duelist. He's well-versed in psi-battles with other rules, AP combat is entirely new thing for him- I doubt there's even a psionic astral plane in DC (there's something of the sort for magicans, though).
So if suddenly brought here by XAVIER- he's doomed, sine he's DRAGGED into infamous battleground, and knows no rules in that type of dueling, where skill pwns brute force more often than not.