I'm probably just dense, but limiting the psionics to a single option, and then preventing augmentations by lack of PP, seems to make Overmind inferior to Natural Mage, by a seemingly large margin, as augmentations are part of power scaling and utility. Would it be such a terrible thing if Overmind granted enough PP to manifest each power once, without augmentations (81 PP). It would give the option of augmentations, but would cost the ability to manifest one of the other powers.
The option to select from mantles might be a nice addition.