Long time lurker, rare poster.
Since the Mantle removes "Independent Character", the Autarch cannot join anything...understood. Does this also change the Autarch into "not a Character"? Therefore, he cannot challenge, be challenged, or produce precision strikes? Looking at the unit entry, I think that this is the case. The Autarch is just left as infantry...not a character at all.
3++ had a great article on using The Solitaire where this observation occurs in the comments but no one ever directly answered or addressed it.
So is a model with the Mantle no longer a character because he is no longer an independent character, losing all the benefits/problems therein?