On Question 1:
I can't imagine psychosis is good for study in general - amongst many other things; and so for either situation you've outlined: the humanities or hard sciences - for all one knows it might be study that has contributed to the psychosis: what this says is that they should be looking for help; and help from someone who importantly knows them and knows how to help - and this will usually mean by a trained professional; in certain cultures this may be stigmatised
Formal instruction in any academic subject is importantly about knowing how to take constructive criticism and being guided; it's knowing about how to put ones ego aside; it's also importantly about knowing how to pay attention - in general, it's all about close study (but of course not limited to solely that).
Think of an athlete - they have coaches; people who know their strengths and weaknesses and so can pace them; and they pay close attention to how one should run or throw.
The same goes for any academic discipline; admittedly it's slow when one wants to run straight-away; but in the long run it's definitely better.
On Question 2:
Intelligence testing is famously quite bad at capturing intelligence; what it's good at capturing is lack; it acts as a rough filter - and this is why it was developed or rather promoted originally; but it doesn't capture real aptitude.
I can't imagine that any subject at a high level can do without sustained focused effort; someone who is good may make it seem effortless - that's the essence of fluency; but it's usually been achieved through rigourous effort; too much rigour is sometimes as bad as too little; talent has to be tempered for it to become anything.
Unfortunately the romantic myth of effortless genius is still something that people want to buy into; and how it's often sold; one should see it as the mature talent; but not how it's nurtured.
But these are general observations; it's not specific to studying philosophy - which is what your question is about.