For as long as Harry and Meghan are on the website, and their children have titles, BP can semi-control their behaviour. There will be things Harry (but not Meghan, because she has nothing to lose by doing so) will even to this day refrain from saying and doing so as not to be completely ex-communicated. Keep your friends close, keep your enemies closer. William would be a fool to cut them off entirely when he accedes to the throne. At that point, they could and, I think, would inflict proper damage if he cuts them loose. They will have plenty of ammunition to make both William and Catherine look bad, fabricated or not. As we can see, facts don't seem to matter anymore (commentary on most world affairs these days).
And I think H&M probably do have legitimate gripes against certain individuals and/or the Firm: you don't get to be a reigning monarchy for 1000 years without knowing how to keep pests or villains at bay. It's probably not 50-50, given who was paying the bills before they left, but I don't think there's nothing there. But it won't be significant if Meghan has been able to move on with only the odd throwaway reference to stuff that happened 8 years ago. If it were anything significant, we know she'd have capitalized on it. After all, she's capitalizing on the most tenuous of claims to legitimacy (hostess, jam maker, doyenne of Montecito etc). Harry, on the other hand, is extremely good at holding grudges so he will nurse even the tiniest slight to the grave. When he demands that apologies be made to his wife, we all know it'll be because - I don't know - Catherine didn't share her Givenchy contacts and left Meghan to wear Reiss to a public engagement some time in 2018.
Meghan is the driving force because none of these people matter to her. Not her family, not her history, not her home, not her memories, not her history - she is free to take or leave them without a backwards glance (and we've seen with other people that she's very good at that), and move her family forward.