The point is that those corners are some of the most important screen real estate, taken advantage by other DEs. Take Windows, for example. Upper-right=close, upper-left=context menu, bottom-left=start menu, bottom-right=show desktop.
Compare to Gnome Shell: Upper-right=settings/account menu (rarely used IMHO), upper-left=activities, bottom-right=missed notifications, bottom-left=nothing.
Where Windows puts something useful in all 4 corners, G-S only has something useful in 2. Obviously one can argue about what is and what isn't useful, but from a purely objective viewpoint, one can definitely say that Gnome-Shell doesn't take full advantage of those extremely important corners.
As for my other points, for example the top bar: how can you deny that it's mostly wasted space? It's 80% unclickable black bar. That's not "nonsense", that's just how it is. Other DE's put something there: the window menu bar, an activities list, etc.
True that I can get an activities list by pressing super. But that's not "at a glance." That's "at a keypress, then a visual scan, then a click to go back to what I was doing." Most other DE's provide some sort of window overview at an immediate glance, ie., an always-visible taskbar.
I think my other points also stand. I don't doubt that some people do use G-S effectively, but that doesn't mean it isn't deeply flawed. If it weren't, then more people would like it.