I disagree, because there is no 'easy' way to know what the most 'significant' changes are. I can think of a few heuristics (e.g. most changed, earliest changed, as well as prioritizing things like header files for C and friends), but nothing that would work universally or particularly well.

Yeah I prefer the review UI to give me alphabetical order just so I can easily navigate it, but I won't read it in that order.

I think the google review tool (critique) would sort C/C++ header files before implementation, even though ".h" comes after ".cc". That's a nice convenience but it's still easy to navigate.