I think you're overestimating how far families married outwith their class. Given the scandal of Mrs Simpson or Ms Markle, how often do you think Barons married commoners? It's the stuff of fairy-tales.
You’re looking at the 0.00001% as an argument why the lower 99.99999% cannot marry into that class - when, in fact, it’s just a matter of math that they cannot do. The marriages of Markle and Simpson have always been more accepted than a peasant marriage between a Catholic and a Protestant in 1950s Germany - just to put your claim into perspective.
Edit: or to put it differently, which of the two scenarios has been more likely in the past 500 years: the daughter of a blacksmith marrying a baron, or the son of a blacksmith becoming a baron through merit?
