Most theses are read by ~4-5 people, tops (i.e. your committee and maybe a friend who helps you proofread it). No thesis is a bestseller. What matters is whether the papers that come out of the thesis are good/useful/impactful in the field.

Fun fact: There are people who try to kill accepted theses based on those. I had a discussion with some theses hunters who get titles removed as a hobby. They claimed that a theses should be an original publication. I disagree with their idea that you should not put ideas from your papers into your thesis, or that you should not publish on the topic while writing your thesis, but I took a lot of care to adhere to high citation standards with regards to that. If you cite well, you can of course keep the title after an investigation.

I've been through one defense (MSc) and have talked a great deal with my advisor about PhD defenses and how these are failed. PhD defenses are failed primarily when a student does not understand where their research fits into the bigger context of the field, does not understand why they chose to use the methods they used, and cannot extend their findings outside of their specific project. Length is not important. Coherence matters, but you will always have a chance to edit your thesis post-defense. Absence of depth can be an issue if that depth is critical for setting up and summarizing the problem. Methodological errors can pass if they're defensible and not ubiquitous, but consistently bad methodology will tank a thesis, especially if you can't defend why you chose the methods you did. Novelty is important, but this can involve revisiting known problems with new methods, and plenty of people get scooped but still manage to defend their theses successfully. Speculation is acceptable within discussion chapters or sections so long as it is within bounds and is supported by the results contained within.

Thank you very much. That was a great summary text to read!