Both Burgundy and Italy benefit from the ability to create new duchy titles at start, which allows them to change money to prestige. Besides, personal demesne isn't that important, because you can mobilize vassal's troops and take scutage.
What I was also thinking about was war. During war, personal demense determines how long you can fight before you are forced to accept whatever peace your enemy wahts to push off on you. The more provinces you have, the longer it takes to forcibly subjugate you. I think demense is important for reasons of wealth, but I also think it important for pure survivability.
I'd rather give Burgundy just Forcalquier and Dauphine Viennois, with Dauphine being the important one, as it allows Burgundy to create titles.
OK.
On similiar issue, I'd give Italy Treviso instead, to give Italy this ability too. Brescia and Montferrato are not part of any uncreated title.
OK.
Scotland and Ireland benefit from being on the side, where they can't be attacked from all directions like France and Germany. But it may be good for balance to make it unified Gaelic crown. But I don't think they need additional demesne after that, because they have actually have huge prestige accumulating from triple-king and very many small duchies as vassals.
I'll test it like that, then, without the additional personal demense.
England doesn't need to be toned down, because England seems rich only because of original William the Superman de Normandie, who could make desert spawn gold. England is province-wise poorer than France, Germany, Italy or Burgundy, which isn't just realized as AI never takes scutage and thus Personal Demesne's value is significantly overrated. If Germany or France put's scutage to 50% or higher, they definetly will have most money.
I'll leave England be, then.