Ultimately the truth will be known, but to your point I wonder to what extent is Comey doing what he has to do to remain in control at the FBI. If he were fired, it seems likely McCabe would be appointed as interim Director, and he very likely would just shut everything down, including the investigation into CGI.
We don’t know all the facts.
That’s my theory too. Comey knows who’s above and below him,. and he’s doing what he has to do.