Granted, I have not been a victim of therapist abuse. However, might it not be scary for some people to have two therapists, in a sense, "conspiring" behind their back? Would it not also make it easier for therapists to abuse clients - because they would basically have an ally to help them get in good with the client again? I also imagine one therapist would be extremely likely to give the benefit of the doubt to the other, which would make it all the easier to gaslight the client.
To me, it sounds like a two on one recipe for disaster...