I don't know if this man will have a better or a worse time in a "normal" prison than in Broadmoor. I would hate to think that he will be put in a wing with other special category prisoners and lauded as a hero, which could well happen.
There are so many different variants of psychotic illness and very few of them could possibly lead to an individual actually harming another person. I too have always understood that typically they are incurable, being "personality disorders" rather than a curable illness. Whilst there are many modern drugs that control the problems there are certainly not "cures".
I have a daughter with this type of problem - she cannot deal with any kind of stress, has little confidence, always thinks other people are talking about her and sometimes imagines things are happening; recently she rang, very excited, and told me that there were armed police in the yard behind her block of flats. I checked with a neighbour and found that this was all in her imagination. She is no threat to anyone, probably not even to herself.