It varies a lot by field, but in many (not all) scientific fields, a PhD thesis is largely a formality these days. Your publication record is what counts. The days where you could get a tenure track faculty position just on the strength of a PhD thesis are long gone.
that's how i understand it. it's a portfolio with front matter, back matter, the papers that got published with some connective tissue between them and maybe some discussion of the things that didn't work out and why.
Depends on the subfields. CS is by publication, number theory varies ("my students can find a stapler" to the dissertation has revolutionary result not published elsewhere)