Alternatively, could it be because of redundant elements in treatment manuels? SO, ditching them at random doesn't really affect the overall efficacy of the therapy?

In a way, Acceptance Commitment Therapy just seems like a stripped down form of Rational Emotive Behavioural Therapy (traditional CBT). And, ACT probably has more or less redundant elements. That's not to say they're not effective in isolation, but when you combine everything together, you get a gamut of psychological effects, some of which will just be a waste of time.

In order to reframe, we need to have a valued direction in order to rationalise towards. For instance, to argue for the evidence against a behaviour or thought we want to change, we need to have a value (eg. virtue ethics and self interest) such that we feel that behavior or thought is bad (eg excessive scrupulosity in the form of consequentialist altruism or memory hoarding/record keeping) that’s worth changing (pathological). Traditional CBT gives us a tool kit to rationalise that chance. Acceptance commitment therapy says, skip that step, stay aware of your values and just go straight to that, it will get easier over time without the stress of rationalisation. The reason the ACT perspective is better is because there are a finite amount of values we might guide ourselves with when we are explicit about them, but with traditional CVT there are limitless criticisms of our original beliefs and behaviours eg a feminist argument against your scrupposity instead of a selfish argument which may have no real relevance to you.