I agree with you 90%. MM arrived with her agent, PR, legal team and accountants all in tow from the US.
Each of them would have their snouts in the trough - likely this would have been a career defining mega financial global opportunity for each of these firms to exploit. They were looking to strike deals left, right and centre - so no doubt whipped MM up into a frenzy with the promise of elevation to the super elite US “A list’ with $$$$.
But they didn’t understand the British monarchy system and how this wouldn’t work. I would imagine that once MM was informed that these riches were now out of reach her head would have exploded!
I do think that H&M had favourable global press behind them at the time of their wedding - I think it could have been sustainable and hugely profitable it they had played their hand differently and they could have had many more opportunities. Arguably the agents did very well with the three big deals - NF, Spotify and Spare - but H&M vexatious, brittle, deluded, grandiose yet talentless personalities squandered the lot.
If anyone should write another book about them it should be called “Squandered” everything from personal and professional relationships, to opportunities, to cash, to reputation. How they have managed to kill a brand in less than 5 years is a spectacular achievement and one which will be a classic case study in marketing, branding, reputation management and communications for decades.