Yeah, Heather's attitude definitely is what has made me fall in love with the character. When she showed up in Englehart's Avengers, she definitely had that stuck up, hollier than thou attitude, however, she was still clearly a good guy. And, before Ba-Bani, that was, as far as I knew, how she was always portraited, treading that thin line. And, for me, she was always such a fascinanting character for so many other reasons that made her unique, and that were not always explored at the depth it should. She is one of the few Avengers with mental powers, a skill that the mutants seem to always hog in their teams. Not only that, but considering that Mantis was merely empathic, before getting the full psychic upgrade, and Sersi was not as adept as others from her Eternal race, Heather was by far the most powerful mentalist in the Avengers armory. Her martial arts skills, putting her almost in the same League as Captain America or the Black Widow. There were not that many like this back in the 70's. Another aspect that was very rarely explored was the fact that, due to her upbringing in the advanced society of Titan, Heather was one of the few female good guys that actually excelled in science. Her current status has acutually made me feel confused. I was never a fan of the Dragon of the Moon retcon, that it was this evil ancient entity that corrupted her. I prefered when the hubris was all her own. The merging with an other-dimensional Heather is, IMHO, yet another unnecessary complication of what should be a much simpler character. I'm still hoping that Moondragon will re-join the Avengers, further exploring her usefulness to the team, as well as the disruption she always brings to their ranks.
As for, what differes Heather and Mantis from the other mutant telepaths, the way I see it, mental powers such as telepathy, teleknisis, empathy, etc...are all part of the potential evolutionary package of humanity. All of us have it, despite it never being fully develped beyond the potential. Through training, Mantis, Heather and a few others managed to unlock this evolutionary potential, granting themselves those abilities in various degrees, however, they are still human. Mutants have an x-gene that sets them apart from the rest of humanity, an X-gene that grants them access to powers that the human race has the potential to develop, such as telepathy, T.K., enhanced physical attributes, etc..., and some far beyond those the human race even has the potential to acchieve, such as fireing devastating beams of concussive force through their eyes, or absorb cosmic energy and fire blasts of energy through their hands, or even controling the weather, to mention a few. to sum it up, it's all in the x-gene.
Peace