Yup, nail on the head. It's the inevitable consequences of ill-thought-through policies with no regard to human behavioural aspects. It's common sense that people will reduce their working hours/not take extra shifts or not take promotions etc., if they're going to be worse off, or not better off enough to make it worthwhile losing their valuable time. Trouble is that far too many people are still in denial about human behaviour and seem to think that people should continue to work more, even if there is no benefit, for societal good - utterly deluded!
I've had clients who've worked for the NHS, i.e. dentists, locum doctors, locum radiologists/speciality nurses, etc., and all have basically done exactly the same, i.e. not take extra shifts, not take job offers, reduce working hours/days, etc., to avoid these tax traps and tax cliff edges. It just makes the waiting lists worse.