If that's true then I think Sussex title should go.
I think the only reason that hasn't happened is that the Queen won't want to remove Harry's Princely title. That would involve a lot of legal arguments and the government would have to agree
If she removes to Sussex Dukedom then they would be Prince and Princess Henry, the Michaels of Kent. The media, especially in the USA and Canada, would instantly name her Princess Meghan, as they did with Diana, and the removal would suddenly seem like an upgrade