Believe in yourself or your supervisor for your own PhD thesis when you feel it is ready for submission?
Towards the end of your PhD studies you should be the ultimate world expert on the narrow topic of your thesis. You should be familiar with all published related research, and have added new knowledge through your own research.

It is your responsibility to convey that knowledge, in your thesis, in a form that other researchers in your area can understand. It is essential to getting your PhD that you convey it in a form that the committee that evaluates your thesis can understand. 

If the examining committee don't understand it, they should reject it. At the best, your writing is not good enough. At the worst, fuzziness in the thesis reflects actual muddled thinking and the research needs more work to sort that out.

Regardless of whether your supervisor will actually be on your examining committee, they are the best surrogate you have for testing your thesis. If your supervisor does not understand your thesis, it is not ready to submit. 

Looking at the bigger picture, the smarter you are, the more academically advanced you are, the more of your time you are going to spend explaining things to people who know less than you and need more explanation than you would. Your thesis is a good place to work on those skills, with an expert audience who will give feedback.