I think you are characterising the difference in emotional maturity rather than intelligence.
Emotionally immature adults are reactive rather than responsive. Their sense of self / locus of control, is externalised in that they require validation from others to feel secure and at the same time also blame others for their bad feelings/behaviour.
They have no ability to self reflect to take accountability for the impact of their behaviour on others and then adapt and emotionally grow.
He’s stuck in the volatile toddler tantrum stage - locking horns, shaming, blaming, raging and flouncing - systematically eroding any semblance of nurturing, interpersonal relationships which are foundational for a sustainable internal emotional life.
I think he had some of these emotionally sustaining relationships in place before he met MM - with his brother, SIL, old friends, colleagues etc - there looked to be warmth, love, respect which got him through his emotionally traumatic and chaotic teens / twenties. But this emotional life line was cut off when he was systematically alienated from his friends and family and where he took on MM grievances. His words and actions stick to his cognitively dissonant script of victimhood but his body, his demeanour, how he physically holds himself tells the true story of his loss - not even sure if the penny has dropped and he is aware of it or not. I can imagine it must be heartbreaking for his father to watch.
I think MM is even less emotionally evolved than PH - I think she doesn’t have a heart or a soul that can be crushed - all of her relationships have been transactional in life. She’s happy to stand on anyone’s neck to get on - all of her ‘niceness’ is studied, contrived and calculating.