Yes I think this is an excellent insight. Dr C perhaps wants to ensure long term sustainability for Sentebale by widening it beyond what sounds like a cosy fundraising gig which enables Harry to do plenty of what he likes.
It's a similar situation with Invictus - the rumours are that they're very keen to widen their activities and PR so that they're not just associated with Harry.
I think we're now seeing some of the longer term consequences of the messy and recriminatory exit from the RF which H&M chose. If Harry had remained part of the RF, sustainability would not have been an issue for either of these charities as his children and other RF members could also have gotten involved, in time. But now, he's not a full Royal, he's a celebrity husband in the US, without the pull or networks he could once bring to bear. So he's less valuable, and his favourite charities have to look beyond him.
It's interesting that the Palace, in setting up Sentebale and enhancing Invictus, were very clever to find Harry activities that were socially meaningful but also allowed him to do things he loves to do - polo, hosting gigs etc etc. Two birds one stone - get Harry doing something socially positive and keep him out of trouble. And the Palace probably also kept a close eye on the charities to ensure that Harry, through misspending or poor behaviour, never got the charities or the RF into hot water.
Possibly Harry didn't fully realise how indispensable this behind-the-scenes Palace work to the healthy functioning of his role as Patron of Invictus and Sentebale, and the health of the charities themselves.