Authors often use beta readers to give them feedback on their work and I think this can be a great way to get a sense of a reader’s experience of the novel. Any thoughtful reader can tell you what they liked, where they got confused, plot events that struck them as implausible, or scenes where the pacing might be off.
But judging whether the story generally meets readers’ expectations and genre conventions and how to solve any problems that exist requires expertise.
You don’t have to hire an expert but it can save you a lot of time and trouble.
A while back, I went to my primary care doctor because of a suspicion-looking skin condition. He examined the area but didn’t make a diagnosis. He sent me to a dermatologist, who told me ten seconds after looking at the problem exactly what it was and how to treat it. It was so easy and straightforward I wished I’d gone directly to him in the first place.
An expert editor has seen all kinds of manuscript conditions and can identify most issues right away. They will almost always have a clear plan of action for you to follow.
My primary care physician could probably have diagnosed my situation by relying on what he learned in medical school and looking at a couple of textbooks and maybe calling up a colleague. But neither he nor I would have been as confident about the diagnosis and treatment plan as I was when I went directly to the expert.