Wait, is she limited by the abilities of her host body? I ask because in order to take over Xavier, she had to use her own telepathy (obviously), but also that she was manifesting solid, almost like hard-light telepathic energy to form energy limbs, which is something Xavier was never powerful enough to do on his own.
Agreed about Cassanova telepathically controlling Lilandra to manipulate the Shi'Ar Empire rather than mind controlling the entire Empire, though. After all, the Imperial Guard turned on her only because they were shown the truth and realized they were manipulated/betrayed -- there's no proof that they shrugged off or broke free from any kind of telepathic control.
In Xavier's body, she still manifested her mummudrai astral body - the form with all the limbs. It gave her telekinesis using the limbs, akin to Lucy's vectors.
In her own body, she had a plethora of other powers - healing factor, a bio armor thing, disintegrating powers that melted Wolverine's arm to the bone, as well as phasing, and much much stronger telepathy that allowed her to casually overwhelm Xavier with ease, while he was being amped with Cerebra.
Cassandra created the body herself using organic materials, and that body supposedly had access to Xavier's full genome, and his full potential completely unlocked, which I assumed was why she was so much more powerful than him and Jean combined while in that form.
When Emma brought her old body back (which was actually Stuff shapeshifted into that form), Cassandra "sniffed" the body, and thought it was her "true flesh", and she planned to re-inhabit it to then regenerate, grow strong again, and then destroy the X-men. Obviously she was then trapped in Stuff, but that scene seemed to suggest that in her own self-created body, she was much stronger and had a whole host of other abilities that she did not have in Xavier's body. I assume by infusing her mummudrai self into Xavier's body, she had access to both his telepathy and her telekinetic psionic body and limbs.