Trouble is, no-one knows your book like you do. No-one knows the characters' motivations. So how can they possibly write a query as intimately involved with the book as you could?
No it isn't easy, but tough shit. If you want easy, why did you become a writer?
scarletpeaches, PMT. That's
Permanent Maniacal Tension to you.
Yeah, but!!!
I'm not disagreeing with your general sentiment. You're absolutely right, no one knows your book better than you. You are close to your work. You know why you wrote it, what you intended by writing it, the exact story you wanted to tell. You know more about your characters than your readers will ever discover.
But, do you know why Susy Q from Texas or John X from Guatemala is going to like your book? Nope. Because you're not Susy Q or John X. Therefore, if someone else reads your book and tells you what
they found compelling about it, you may just have a better idea of what another outside reader -- i.e., an agent or editor -- is going to find compelling. They might be able to articulate it better than you, who is very, very close to your work.
Case in point: Miss Snark's Happy Hooker Crapometer, in which it was proven that some of the best queries yielded some of the worst actual pages, and vice versa. You can end up with a crappy query letter, because you just don't know what is so great about your book, but you may still have a great book.
This is also why Miss Snark says she values the first five pages of a manuscript in her submissions -- because you can't always tell from the query what the book's going to be like. For those agents/editors who will ONLY read queries and won't look at samples of the work itself, you'd better make sure your query is freaking brilliant.
If that means finding what makes your book compelling to readers, I say getting the
basis of your query from someone else is a smart idea, if you can do that.