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.

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)

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.