This is a very fair and valid question.
I have seen two psychiatrists, and about 10 psychologists, I had never seen a psychiatrist until late last year, and i did not get along with him very well at all, in my opinion he was absolutely hopeless, and i have no idea how he was even a psychiatrist.
But that is not the question lol, i actually point blank asked this particular psychiatrist what it was he did exactly, his response was he assesses my mental state, and prescribes medication, i said to him that my psychologist can do that and my g.p can prescribe medication. he didn't have an answer for it, so i did not see him.
But with the new psychiatrist i learned a little bit more, they are trained to be able to interpret the different mental health issues present in a patient, they are also able to radically introduce medications when needed, and to monitor the progress of those medications, in a far more understanding way then a psychologist, they also if you look closly at there specialities, will be focused on certain catagories of mental health, example some specialise in tretment for BPD, some are specialists in bi-polar etc etc, they actually undertake further training to be able to work better with the sub catagories of mental health. They can and still will treat patients which fall outside of their speciality but a really good one will know others in other fields who might be better suited to what you require treatment wise.
A psychiatrist is also able to order certain tests to be done that your g.p or psychologist can't order.
A psychologist works more on therapies, and monitoring of medications, they also will specialise in certain areas of treatment plans, umm like they might mainly focus on ACT or DBT they should also be in contact with your psychiatrist to be able to closely work towards a better wellness plan. some psychologists are more like counsellors, and then you also have clinical psychologists, i am not too sure on the difference there but i think clinical can also adjust your medication levels if needed.
Hope this helps, it is just what i have picked up over the last 6 months
Oh the 10 psychologists i have seen 9 of them were about 6 years ago i found a really good one recently
thank you