Psychiatrists have biases. There are reasons some psychiatrists are strongly in favour of and are ready and happy to do MAID assessments. We come with biases.
If you're asking what the data says about capacity assessments, it's very easy to sort out who's extremely psychotic or profoundly depressed. It's very easy to sort out who's doing really well and is quite capable and rational, which would be the majority of people. What's complicated is the grey zone, and the grey zone is substantial. The data says that about 75% of psychiatrists will agree on what they're seeing, and if you have 25% disagreeing, that's pretty significant.
I frankly view the capacity issue as a red herring. I've thought this for a long time. People are focused on the idea that we have to decide whether they're able to decide. That stuff is done every day in psychiatry, and it's called a capacity assessment for treatment decisions. Insofar as you're calling MAID a treatment decision, then this fits into that category.
To say it's somehow special or different does not, in fact, reflect the reality of the day-to-day work of mental health care. Are some people better at doing capacity assessments than other people? Absolutely. If I have 40 years of experience, I'm going to see things differently than if I were a fresh grad.