How do you explain OH's son becoming dependent on his wife's family if the strings of his own were so irksome? He no longer even has the independence of his well paid job know.
Children do what they know. Children's expectation of boundaries is a learned process. Unlearning can take time. Unlearning is not always achieved, particularly if the learning started very early on in the child's life.
It is not unusual for a couple (as in married/romantic) to have a shared experience of high parental expectations of control and similarities in family dysfunction . It can be an element of what brings people together. In the sense they can feel both understood and able to understand within the pairing, to a degree that can be harder to achieve with people from more "normal" families.
Plus people who do not have similar experience of family dysfuntion can (understandably) run a mile when they realise just how messed up you and your family are. Making your prospective romantic pool somewhat more limited from the get to.
For example both my husbands, (despite all three of us coming from different countries and in one case a different continent) came from similarly dysfunctional backgrounds to myself if you view it specifically through the lens of parental expectation of control and weaponising of their children.
Of the three of us I am the most successful at recognising, describing in words and resisting (albeit very imperfectly) that specific sort of dysfunction. In part because their family dynamic was fixed from birth whereas in mine the dysfunction was a much later flowering. In part because ... I have had more practice thanks to jumping from the frying pan of my family, into the pot and the slow cooker of both of theirs. They have experienced the dynamic twice, via their family and my own. Whereas I have experienced it three times with my own family and spouse's' family X2.
You can keep choosing what you know at least as often as not. You can heed your gut and leap for the purposes of escape, survival, and find yourself in not so dissimilar circumstances due to the siren song of the familiar. Like a kind of groundhog day, just with new faces.
The advantage of escape into a similar looking jail, perhaps only advantageous in the sense the new one has more day trips out of the grounds allowed, is that you do not experience the same emotional connection to or filial piety towards a spouse's controlling parents. Which can lift the fog and allow you to see that kind of choke-hold love for what it is and better understand the strategies employed when it is practiced. Sometimes to the point of effective anticipation and a more successful heading off at the pass than you were able to achieve in the past.
Some people eventually move on to escape from that sort of controlling element altogether. Other's can end up in largely similar, if not actually worse, example of dysfunction with the spouse's family. Some strike a balance between the familiar and the unbearable by moving to the same dynamic that is just enough degrees lower in controlling element to make it an acceptable compromise for them between the fear of the unknown and the yearning for freedom.
At certain points over the last 30 odd years I have been all three of the above via both my husbands. I didn't get a dummies' guide to help me navigate the cards I was dealt at 16. So it has been a messy, inelegant and often very "2 steps forward, 1.89 steps back" sort of path to the destination I was trying to run towards. I am free now. Or at least as free as anybody can be when they are lugging this much baggage on their trudge through life. But it took a long time, some extended wandering around in cul de sacs and several parental deaths to get there.
Hypothetically speaking, if the OP's son's experience of "own family" dysfunction has been similar to the sorts of dysfunction I am referring to, then refuge sought in a not so dissimilar family dynamic would be confirmation, rather than negation, of a known pattern.