I'm often sceptical about BG but I find that analysis entirely believable. Coincidentally I rewatched the engagement interview this morning - sometimes it's helpful to remind ourselves of what they actually said rather than what has been reproduced and distorted by the media.
From the interview several things struck me. They only had two dates before they went to Botswana for five days where it seems his feelings were cemented. I've always said their relationship had the hallmarks of a holiday romance and I stand by that.
When asked how long they had been together she tried to make it sound longer, (two years), he corrected her. I don't believe that someone would not know how long they had been involved with their partner, particularly for so short a time and when they had just discussed the date they first met.
MM in particular talked about visiting the Commonwealth. When talking about their planned work H said "There's a lot to do". I think they both had a genuine desire to do the Commonwealth thing. I think what happened to change things was Archie. And tbf, that isn't unreasonable, the things you can do as a family are not always the same as those you plan as a couple.
I don't believe she misled him as such, I think she realised she had the upper hand in their relationship and didn't have to follow through on anything she didn't want to.
Further to that, H seems to be strongly influenced by others and looks for leadership. MM is a natural leader. Perfect storm.