Leblanc Question

So what is the reasoning behind Leblanc's ult cool down? Isn't 40/32/24 second cool down way too good? Not to mention Leblanc also builds CDR items as well. It seems a bit ridiculous how short the CD is allowing her to have kill pressure 24/7 and guaranteed escape for the majority of the time.

Not much of a mid laner but from my experience even if I out play her by dodging her combo she still gets away and comes back with no repercussions on blowing her ult to capitalize on. I do realize late game her team fight potential drops but she can still dish out mad amounts of damage late game and is still a high priority target.

The only other assassin in comparison I can think of is Akali, but at least she has a terrible laning phase to compensate.