USP isnt a plastic gun, only the lower frame is polymer.
Fat and blocky is good. It sits in my hand nicely. Maybe you
have hands which are "lady-er" than us ladies 
"Plastic guns" is merely a colloquial reference to firearms that
have major components made out of composite materials; the USP
would fit that definition since its frame, as you've noted, is
polymer.
Out of the dozen-or-so polymer-framed pistols in my collection,
the only one I would consider somewhat uncomfortable to hold is my
Glock 34. It is a very accurate gun, but the blocky grip with
its excessively raked angle requires me to adopt a different and
somewhat unnatural hold when I shoot it.
The most comfortable and natural-pointing plastic gun in my
collection is also the one I carry: the CZ 100.
