People forget that, years ago, air stewards/stewardesses were well educated people who could speak more than one language. It's not like that now, all sorts become air hostess but it would have been so in Carol Middleton's time.
Carol Middleton has done very well business-wise and home-wise.
Kate's father comes from a well established business background.
The Middletons are more 'Cazalet' than 'Downton' but what's the problem with that? Kate has easily slotted in since her marriage but she had a good few years preparation. That does help, also the fact that Kate is (or seems), so gentle gives her a sympathetic profile. After a few years of being 'royal', and three children, I've no doubt she is part of the royals.
I know this thread isn't about the Cambridge's but they have been mantioned.
It's very unfair to compare Kate and Meghan, they're very different people but each are good in their own way.
I would hate the negative press to push the Sussex family to live in America or to contribute to them breaking up. My opinion is that they are pretty good in most respects, nobody is perfect.