come on man, beating arkham knight in performance/visual return is hardly an accomplishment. mad max was also a retooled ps360 title that kind of got stuck in development hell so its also an uphill climb.
I said Mad Max because that game was praised for its performance and rightly so, it does run well on a very wide spectrum of hardware, I would agree that it is not exactly unexpected considering how "last-gen" it can look.
Just Cause 3 however is a different case where I was genuinely surprised to find out how well my game ran with everything save for shadows cranked up to the max.
Of course that does not mean the game makes the absolute most of their targeted range of PC hardware, for all I know there may be significant performance gains possible but as things stand I find no reason to complain pertaining to performance, and to reiterate this game looks fantastic.
My only gripe is the flickering really, I don't know when it will be fixed. It's not game breaking but certainly stains the otherwise beautiful scenery.