Yes, the corners are useful for sure. Unless you are working remotely (i.e. have another desktop in a window), in which case they are not really corners and become a nuisance (i.e. they activate overview in the remote desktop when you go over them on your way somewhere else). But, yeah, horses for courses and all that. I certainly understand your point. In fact, you could have hot corners in Gnome 2 with compiz.
On the point of the workspace switcher, it can be made bigger (customisation benefit), it is flushed against the edge so, unless you are working remotely, it's a big target, just like the corner etc. Also, it can be moved anywhere (another benefit of customisation) - mine is in the upper left, next to the menu, for instance.
But, one of the main benefits of the workspace switcher is visibility. It is literally zero effort to remind yourself where stuff is at any given time. This is completely gone from Gnome Shell.