I think Saturn Girl is the closest telepath to Xavier. She's created life forms, scanned the universe for life, and is known to be the most powerful telepath in DC. I think. I don't see anyone on her level. Not even Martian Manhunter.
Also, the arts of TP combat in Marvel and DC are pretty much different (I'm talking about combat tactics).
The Astral plane is mostly natural to mages in DC, DC telepaths' level of expertise combatwise are mindscape bouts.
So in fact there need to be clearly declared rules. Both are using somewhat different tactics in their respective universes.
Without it, if Xavier brings fight to the Astral plane, Saturn Girl would most likely be confused as she's not used to that (though she's adept in mindscape\hivemind stuff).
Not too much of handicap, though, as mindscape and astral battles represent sometimes similiar tactics.