Are all power-born mages insane?
Not necessarily all of them are clinically insane; some of them are merely extremely dysfunctional, such as the example mage I mentioned above who can only speak in rhymes. The extremely powerful ones are usually massively disordered and barely capable of functioning in society. Generally, if you’re going to play a power-born mage, they’re required to have some sort of dysfunction, disorder or derangement. (Look, I made an alliteration!