Rhein was only a lower Lexmechanicus before he left the Adeptus Mechanicus - with that, he has only basic knowledge how to deal with the cyberspace and, obviously, AdMech rites. Most of his knowledge was gathered as his life as outcast - and thus, yes, I thought him having a much narrower but deeper set of disciplines. His main expertise are weapons, warmachines and tools of destruction. He has quiet a knowledge about coding and little about bionics, too - but more of the crude and functional kind (and usually that's more than enough, because he's implanting weapons of all sorts). Yes, he's pretty flesh-loving... and not very in line with the AdMech discipline of giving up emotions and feelings. But I have absolutely nothing against letting Azrael handle the biologis-field.. and Rhein seeking his council. That's just making things much more interesting.
Does this work with you?