Mentalists do kind of lend themselves to abusive builds simply because a majority of characters in the milieu is going to be next to helpless against them. And oddly enough this is true to the source material. Xavier is an omega level telepath; if he wasn't an NPC most issues of X-Men would be pretty boring. The only thing that usually stops him is his strict moral code against invasive mind attacks. Magneto has to wear a hat specifically because of Xavier.
In the comics the defense against psychic bad guys is almost always at least an Ego push and, more often, it's teammates verbally helping the target to resist/shake off the attack, or figuring out the attacker's vulnerability. That's not built into the Hero system. It's up to the GM and players to figure out how to account for that--a sudden breakthrough in psychic helmets and jamming technology would be an obvious place to start.