the more I inhabit my own brain the more I become convinced that the two parts of the brain you distinguish here are actually largely the same

They may well be for you but they aren't for me in the slightest. There's my emotions and then there's my pattern-matching/learning brain, and while the pattern-matcher does feed data into my emotional brain, the emotional brain is very selective about what stimuli it pays any attention to and very slow to change its idea of preset patterns that absolutely need to be responded to, however different the current context is - all this cliched psychoanalysis stuff you hear about responding to people as if they're one of your parents is actually perfectly true, it's just that it only becomes a problem when you have duff parents!