Yes, but so far they've gone down the crapper in a way that does not seriously infringe on Mio's mental integrity. Something that will not be the case if we plug the super shady sealed evil into her brain. Maybe it's different for you, but I don't particularly enjoy reading about someone's protracted mental erosion and collapse at the hands of a nebulous and insidious malevolence. While obviously it probably wouldn't be something that we couldn't get out of, but at what cost? In developing the chakra arm we risk simple death at worst for pretty much equal, or arguably greater, benefit. With the sealed arm we risk all of the above, as well as completely locking ourselves off from one of the most broken powerups in the setting (sage mode) as well as a variety of other possible effects of corrupted chakra. I simply do not think the benefits even remotely outweigh the almost certain risks.