I think PM was way way over the top with his opinion - he is so annoying at the best of times he just talks over everyone . Even if he had a point his delivery would make anyone stop listening.
Just my opinion but I think Harry and Meghan heard that Archie wasn’t going to be given a Prince title when Charles became King.
This sent them over the edge as it was a new rule that specifically affected them as part of Charles s plan to slim down the Monarchy.
Everything has gone downhill with his family since this point with Charles being the main target.
It’s always hard to stomach being the first one disadvantaged by a new rule