I remember listening to Writing Excuses and they were talking about this. Yes, it's true, but given enough time and experience, it is possible to regain some, if not a lot of it back. For me, I've found this to be true. I can sometimes actively ignore some flaws because I know their relative importance to the story as a whole isn't all that great.
With some mechanical issues like grammar, that's simple to fix, so things like that, though important in some ways, is meaningless in others.
Other times, I can switch gears, and simply become a reader again. And for me, how long I can maintain that reader's mindset becomes a test of if I'm enjoying the story or not. If my writer brain is constantly turning on, and I start to nitpick that's when I know I'm not engaging with the story, which can be an indication of an issues with the story telling. Because if I'm engaged, I'm along for the ride, and I'm suspending disbelief.
Now there are limits, but I have thoroughly enjoyed many a flawed story simply because they were engaging.
I find I never read for enjoyment. But that has been true most of my life. When I read, I am always looking at it for how it all works. But, sometimes, I do shift out of that, and almost always it is because the story is so compelling I stop noticing its parts and just start going with it. I like it when that happens. But it does not happen often.
Chapter length to me isn't as important as the actual storyline. As long as the story runs smoothly and keeps the reader satisfied then you shouldn't worry about how many words or pages each chapter is. Most of my chapters end up to being around 8 to ten pages long, but sometimes they run shorter or they run a little longer. I only emphasize that you shouldn't drag the scene too much so that the reader looses interest.
I agree with the Tolkien comment that Bilbo's birthday scene was way too long. Though I have read the Lord of the Rings, and the Hobbit several times, that first chapter of the birthday scene in the Fellowship of the Ring was dragged out and kind of boring to me. Even the meeting in Rivendell seemed to drag on for me too. Even though it was needed to learn about the quest and such, I believed it needed something more to it to make it interesting.
To that I say this, make the book how you will, but remember that it's the readers that you need to make happy. It is them who you must entertain and want to finish your product. So I say good luck and keep plugging away!