Article-based PhD and advisor's (new) role?
This topic is near and dear to my heart, as the number of days until I finish exactly such a thesis is measured in a single digit number.

If you field is dominated by journal, rather than book, publications, I think its a vastly superior system, leaves you better prepared for what you'll actually have to do in the future, and leaves your CV in hopefully a stronger place.


  But with an article-based PhD, it seems that the active approach in
  editing co-authored journal papers is essential, and in effect writing
  a big part of the dissertation for the student. I realize every case
  is different.


This has not been my experience - even the most active members of my committee who are co-authors on papers can't really be said to have written a significant portion of my work. Generally speaking, I would send them a fully fleshed out draft paper for their comments (which is exactly what I tend to do as first-author on a non-thesis paper), and then we'd iterate through the draft several times as they tinkered with language, added their own pet sentences, asked for additional analysis, etc. But the paper, in its final form, is very much dominated by my work and my writing.

One of the keys may be to not wait until the end of someone's graduate career to work on their writing. If someone needs you to fundamentally rewrite massive parts of their dissertation papers, in my mind they're not ready to defend. They should be at a stage of maturity where they can produce largely independent writing, in need of only the usual modifications a co-author would provide to a manuscript.