Dear LJ Moss
Thanks for your question.  It’s London Book Fair this week, so time is short. I hope you’ll therefore forgive me for keeping my answers brief.
I would say that editors have less time to edit than they did previously.  Editorial teams are generally smaller, which means fewer people to work on the same number of – or more – books. Also, the pace of publishing is simply more rapid these days (like life in general!) Twenty years ago, it wasn’t uncommon for an editor to find a manuscript that they liked and to work with an author on it for several months before taking it to an Acquisitions Meeting.  (The Acquisitions Meeting is the meeting in-house at a publisher where it’s decided which manuscripts will be bought and published.)  That sort of nurturing of a writer would be almost unheard of now, not because editors don’t want to do it – I suspect most would love to! – but because there isn’t time these days.
The other change I think has occurred is that, whereas previously editors generally decided what a publishing house would acquire, that ‘power’ has shifted towards Sales, Publicity and Marketing.  
Yes, one of the key things on which Greenhouse prides itself is working with authors editorially before we submit their manuscripts to publishers.  Both Sarah and myself have vast editorial experience as we have worked in some of the UK’s major children publishing houses.  Both of us were Publishing Directors before becoming agents.  We can see the potential in raw material and know what it takes to get it to a point where an publisher will want to acquire it.