Ok, well maybe never is a bit strong, but there are several good reasons why you should try not to compare your polished manuscript to a traditionally published novel. Most importantly: It. Will. Drive. You. Crazy.
Of course you should read widely, and reading in your genre can make you aware of certain tropes and issues such as pacing and tone. Reading books by good authors is inspiring, and can fire you up with enthusiasm for your current work in progress. But it can also make you want to throw it in the bin/set fire to it/use it to line your cat's litter tray. Why? Because most books have a team of people behind them, rather than just the author. Unless you have hired a multitude of publishing professionals to go over your manuscript with a fine tooth comb, it's not going to be in the same stratosphere.
Publishing companies hire commissioning editors, copy editors, fact checkers and it's not because they're trenchant socialists eager to give everyone a job. They hire just enough people to ensure that they can produce a quality product that will make consumers part with their cash. These people are necessary, and any self-publishing guide worth its salt will tell you that if you're going to forgo the traditional route you're going to need to hire at least some professional freelancers in to help polish your manuscript.
A team of professionals will point out weak points, repetition, inconsistencies, and points where the plot needs improvement. There's a reason why authors usually thank their editors in the acknowledgements section.That doesn't mean that you don't need to edit, though. Your book should be as polished as possible before you start querying. But if you're plagued with self doubt every time you pick up a good book, you should remember that you're just one person. And maybe you should cut yourself some slack.