Even though she was a member of the aristocracy, Diana was still considered a commoner insofar as she was not of royal birth.
Technically, Meghan is a princess since she is married to a prince. I believe on Archie's birth certificate she is shown as "Princess of the United Kingdom". However, since her husband has a royal dukedom she is known as a Duchess (a royal dukedom outranks a Prince). Were they to be stripped of the Sussex titles she would be Princess Henry. The Princess of Wales was still a princess before being PoW for the same reasons, despite the fact she had the title of Duchess.
I really did have a lot of time for them at first and I did feel she got a raw deal by the press (if the DoC did something it was marvellous, whereas if the DoS did the same it was scorned). However, she has now turned this into a proper whinge fest based on racism (I never saw her as a woman of colour, I saw her as someone H loved) and other imagined slights. I cant help thinking that the way she has been treated is a reaction to the way she has behaved - not because she is of colour (her mother, for example, save for her involvement in this docufantasy has been dignified and gracious and I have always admired her) but because of her bleating self-obsessed, narcissistic, demanding way of conducting herself. She's also full of BS and the story changes to suit the agenda.
I think the King has behaved with remarkable restraint. I understand he will not tolerate anyone making negative remarks about his son. But he is a father first and King second. He must be very very weary of all this and very very sad that his younger son seems intent on a path of destruction that even his ex-wife would not go down. I do not imagine Diana would be proud of the way her youngest has behaved.