I'm not sure there was much of a goal other then to quickly get a book out before the Sussexes became yesterdays news, preferably at the same time as
The Crown comes out.
As for why he's such a huge fan a Geidt, who knows. Maybe they personally know each other or his sources were some of Geidt's employees.
As for his hand-holding of Harry, I guess we all have our "pet" royals and Harry might be his. I doubt their mutual Netflix connection would be of that much sway to the point he was encouraged to romanticize Harry's character quirks/flaws.
But clearly this was more written as an editorial and less as a factual textbook. I think you learn more about Lacey reading this than you do about the BRF and Sussexit. But insight into Lacey's mind is interesting in it's own way.