What a great question. I do think a combination of therapies can work really well, under the right circumstances. I'm not sure I would have said that at the start of my journey. If my T had suggested that I supplement my therapy with, say, group therapy or DBT when I started with him, I'm sure I would have experienced that as rejection. Now, however, as my dependency on my T turned out to be a bit of a negative experience, I think having other resources to turn to can be really empowering. I think the muck I got stuck in was due to the experience of having only one therapist and the dependency issues it brought up for me. That and my therapist's inability to help me through the muck. Having only one therapist is the prevailing model of psychotherapy. The standard thinking is that two therapists often leads to the client splitting. I can see how that would happen and I can see how I would have been prone to do that at the beginning of my therapy though I don't think I would do it as much now. Awareness of the splitting can be a great tool to work with.
Since "threes" are generally a difficult number of people, what about having three therapists (making the group total 4)? It could be set up that way at the outset, that they all know about one another. Clients would be informed about splitting at the outset so that they would at least be aware of the possibility that it might happen. You could see each one once a week so you'd have support 3 days of the week. If you spread it out, you wouldn't have to go more than two days without support. You'd have the experience of different personalities and you'd be able to compare and contrast to see what works better for you and what feels best. It would almost be like having three parents to go to.
I think having only one therapist is wrought with lots of pitfalls just as having more than one therapist is wrought with pitfalls. Different pitfalls but isn't that true with everything, like the therapist note disclosure article highlighted?