Drive is needlessly complex. On my laptop I have folder structures. In zip files and tarballs you have structure. You even get hierarchy in a CD.

Trying to find your way around Drive (esp. when sharing between enterprises) is a nightmare for me. Google could cement some really good mindshare if they made shared folders/docs more intuitive.

Flatness can result in much more overwhelming complexity.

I suppose that depends on what you mean by complexity. I prefer lists to trees, in general. After I reorganized my Dropbox into only 1 layer of folders, I've found it much easier to navigate. But hey, that's just my anecdote.