The thing is that no where have they stated that they'd *not* be continuing the roles they already have in place. There is no indication that any of the roles they have now will go by the wayside and need someone else to pick them up.
This is what I think is a huge misconception in all of this. They'll not walk away from any roles, charities or patronages that they already have but perhaps not take on so many more going into the future. Its explicitly stated that they plan to keep on supporting the Queen and the monarchy and also launch their foundation. There'll be more time "away" to focus on their family.
but they are meant to be full time. How can they do the Commonwealth role, which will involve travelling and meetings in London, if they are trying to earn a income, probably in the US and Canada? How can they keep on "supporting the RF," when the queen is gone and Charles is now reliyig on WIll and Kate and his increasingly elderly set of cousins and siblings...
THe difference was obvious to me when the QUeen took Meghan to an engagement early on and she and Harry were thrown in the deep end with royal work. The queen was willing to give Wiliam and Kate some time to themselves but by this time, now, the time isn't there. She is getting older, Philip is retire and frail.. and not able to do anything much. the Sussexes were not going to have the chance to move into royal life slowly... and Harry should have realised that.