I think Meghan saw herself as a combo of Diana and Princess Grace of Monaco, America's 'original' actress-princess. I think as such, she saw herself 'eclipsing' all other royal women (ie, Kate) in popularity and publicity. She didn't reckon with Grace's dignity and style and Kate's position as wife of the heir presumptive (prior to the late Queen's demise) as factors in their popularity AND their places in the hierarchy and the PR machine.
I think she expected a Hollywood style publicity machine working on her behalf as well as thinking she was going to have 'clout' as Harry's wife and as a 'celebrity' in her own right. I also think she bought into all the publicity around the engagement that trumpeted her as bringing 'fresh air' and 'American point of view' to the monarchy. I think she was very surprised to find she had no clout and that her ability to effect change was 'nil' and that she wasn't going to be allowed to capitalize, a la American Capitalism, on her position, either. Instead of adapting to the new life she chose or exiting with grace, she grabbed Harry and flounced.
I think Harry is a weak, spoilt man who thought he found a woman who would fight his battles for him. How much he may have deceived Meghan as far as the reality of life in the RF vs what she thought it would be, who knows. But I do believe he wasn't honest with her, for his own benefit.
At this point both of them are angry things didn't turn out the way they wanted or expected them to and they're bent on justifying themselves to themselves even if it means tearing down their own families.
It will be interesting to see what they're going to have to say about the Hollywood/Celebrity circles once those people get tired of them or have decided they've gotten their 'money's worth' out of them. Will we have "Harry & Meghan Part Deux; How Hollywood Screwed Us Over"?