So, let’s assume you kept re-writing…
In Beta, you need to re-write your novel as many times as it is necessary. Some authors are doing two re-writes and they’re done. Some authors are re-writing 6-7 drafts. You will know best what suits you.
When you get to a point where you feel satisfied with your novel, both story and style, it’s time to put to work those friends that have agreed to be your beta readers. They have the advantage to be your first readers and brag about it when your name will shine in the history of fiction writing, while you have the advantage of fresh eyes reading the story you’ve worked on for so long that you can’t be objective anymore. And anyway, it’s your child. Even if it’s a monstrosity, it will always be beautiful for you. You need those fresh eyes.
It is what in UX Design is called usability testing. You’re creating this new product (in your case a novel) for users (readers), not for yourself, so you better test it before launching it.
The beta readers come back to you with their feedback and not all may be nice to hear. Remember that they’re your benevolent readers. And imagine what would it be to have some readers who don’t care about you and your writing endeavours. Their criticism would be even harder to hear.
So, pay attention to your beta readers and if necessary make some changes to your book. Do some re-writing, some re-thinking. Ultimately it’s your book, your decision. But you need to be realistic and do what’s best for your story.