I'd argue that Aquaman is DEFINITELY Xavier class or above in raw power, he just doesn't have the experience to utilize it. I have to say, breaking into a world class mentalist like MM without even TRYING to is really a huge feat. I have to say that puts him WELL above Psylocke. The whole thing with Rogue's absorption powers is rather irrelevant. It doesn't necessarily tell us anything pertinent about Vargas. After all, she couldn't absorb Juggernaut's powers because they were magical, so, since Vargas is so shrouded in secrecy, perhaps the same is true of him? Either way, it really doesn't have any bearing on the matter at hand.
Him wiping the floor with Rogue, well at least that gives us something to compare. To do so, well, Rogue was class 50 or something, right? Heck, Aquaman has gone toe to toe with class 100s on a pretty regular basis. In fact, he and his son beat an entire team (the Deep Six) who had given Orion trouble one on one. He's also tangled with Lobo and come out of it alive....I've got to say, I haven't heard anything about Vargas that makes me say "wow, Aquaman can't beat that guy."