That question is a huge one. RFT seeks a broad understanding of cognition. In the long run it could be more important than ACT because if it works the whole of psychology could change.
RFT is developmental, contextual, and behavioral. It gives you ideas about what to change to make things happen. It is so basic that it goes all the way down to animal behavior and human infants; and yet so broad in scope that it has clear implications for our understanding of social processes or such human activities as religion.
We have never had an empirically adequate behavioral, contextual account of cognition. Now we have at least the beginnings of one and it seems to be braking down the artificial barriers between cognitive and behavioral science.
The theories underlying CBT and CT are not like that. They have relatively low scope and they emerged typically from clinical concerns. They do not pretend to be the functional equivalent in cognition for what “behavioral principles” are in non-verbal behavior.
You have to be impressed with what the traditional behavior therapists were able to do with traditional behavioral principles, in part because these principles emphasized manipulable contextual variables. Imagine what we might do with a theory of cognition that emphasized manipulable contextual variables, if the theory was relatively adequate. Maybe a lot.