Hmm I'm not sure I would agree with him/her. That's like saying all books should have lots of pictures and few words. Whilst that would be fine for children's books it would not work for all. I imagine the reduction of average time on site has a lot to do with how much rubbish there is out there and people are adapting their ways to quickly sort the wheat from the chaff.

To continue the book analogy, what do you do when you are browsing for a book in a library ? You look at the cover, title, back, read the preface, table of contents, flick through and get a feel for the pitch and style. At all points you are assessing the book and working out if it is worth your time and effort. If it, at any time, fails this test you put the book back on the shelf. With a site you have just seconds to convince the visitor that it is worth progressing to the next step and as long as you keep delivering the goods at each stage then the depth and complexity is immaterial. They will only leave once they have found what they want or you run out of content. Define your target and build your site/page just for them.