Outlet/Switch screw terminals seem designed to prevent wire J-hook from being attached
Yes.  Those misfeatures are actually features. They are designed to help you keep the wire captive and in the right place. 

First, there is a hook designed to hook the existing wire  (i.e. the short on the right side) to help you make the J-hook more than 180 degrees to make it captive on the screw. The idea is now, you don't need to use a needle nose pliers to make that final over-180 bend. This won't make any sense if you're making the J-hook too short to benefit from this feature. 

Second, it helps keep the wires "trapped" under the screw, so you don't have it slip out from under and fail to notice it if you are working quickly. 

This "Trapping" is especially helpful when using stranded wire, which tends to squish around and fray when tightened.  I use a lot of stranded wire, and those things are a godsend.  As the screw gets nearer to bottom, these gates will fully entrap the wire so it can't frizz out of the hole. You still need to give the strands a really sincere twist, but it helps.