I agree with much of what you say.
What KC could do is make the Dukedom a lifetime one like the Duke of Edinburgh. H has other titles e.g. Earl of Dumbarton that Archie can inherit.
We know Lancaster, York, Cambridge, Cornwall and Edinburgh Dukedoms have or will revert to The Crown when the current incumbents die. Being able to appoint them on a lifetime basis going forward keeps them recyclable for those highest in the LoS.
WRT Prince and Princess titles, KC could issue letters patent now that going forward only the children of the reigning monarch and children of the heir receive Prince & Princess titles.
It would not change anything for existing prince & princesses but would mean Charlotte and Louis children would not be prince or princess. It would save an argument when Louis & Charlotte are older.
If applied retrospectively (it wouldn’t be) it would mean Beatrice, Eugene, Louise, James, Archie & Lilibet would never have been entitled to use prince or princess.
In someways Meghan might like H to lose the Dukedom so she can call herself Princess Meghan. She would never use her correct title Princess Henry.