I'm interested how good it is when it's published to judge what 'uplift' there's been for the celebrity angle or whether it should have been published at all.
I expect the public will love it. I'm conscious that some of my in laws love Dan Brown and think he's brilliant. They read one book a year and think it's really good. Not criticising but conscious how subjective things are.
On the face of it, the publisher's business is sales and I expect the celebrity authorship will help sales as PPs have said.
My daughter enjoys Walliams' books and she doesn't think they were worse than books by non-celebrity authors she enjoyed for that age group (I've no idea what, if any, help he had in writing the books).
I'm not sure there is a firm 'pool' of money that would disadvantage unknown authors if celebs are published with big advances. Even if the publisher has a relatively fixed signing budget, I expect if celeb books earn back enough of a return, a celeb book that sells well could lead to a larger subsequent budget. I suspect it could be a little complex though happy to defer to someone closer to the publisher/agent interface.
Putting aside being even-handed, I'm infuriated when I read celebrity books get large advances and find it worse when that big advance relates to a book that is awful.
It's odd that celebrities from other fields (actors, comedians, social media, musicians and so on) get to sell fiction but there's less impetus to put a fiction author in the latest Hollywood blockbuster, headlining Glastonbury and so on.
I've read the SoA analysis and pulling together other research, the industry has the unbalanced returns that you might expect given the market structures -
Amazon - wow but hidden. To be fair, the platform they've built and the relative innovation or purchases of Audible, Kindle and then KDP for self publishing shows some insight.
Top publishers - around 25% 'profit' (vaguely recall 25% but the final figure could be wrong and certainly better than authors and bookshops);
Bricks and mortar bookshops - disastrous though supermarkets find it favourable with preferential terms, low overheads and positive cashflow; and
The average income for published authors is around £8000 pa with averages skewed towards to big earners.
SoA say this is unfair though I think this probably reflects the market structures and power. It's all a bit rubbish though for the writer.
I find it interesting the industry seems to put a premium on new authors even if unknown relative to those already published, to the extend some agents seem to be advising sometimes using a pseudonym. A few bestsellers seem to have had success with a fresh persona.