I disagree a bit - gull identification often isn't possible without really going into small details. The recent gull book (photographic guide of Gulls of the World by Olsen) has tried to be as concise as possible (on average ~4 pages of text and ~4-6 pages of photos per species) but
I think it just doesn't work that good as it in one way oversimplifies things - that can lead to overconfidence in identifying difficult plumages in situations when maybe the ID is not reliably possible?
So to me it is the opposite - I would love to see that future Gull book to be like a spiritual successor to the Olsen & Larsson 'Gull bible'- a book that gathers all current knowledge on WP gulls as detailed as it possible in a book format. Of course it will depend very much on the layout and structure of the book how user friendly it will be. I agree that the Olsen & Larsson book has some flaws in that regard and that makes it very overwhelming at first and not very exciting read - I think I needed some 3-5 years of having it on my bookshelf until I could finally start to enjoy reading it