correct. an open world game CAN be 60fps.
in this comparison that you are making though, we have one case where gameplay IS expanded, along with the pretties (open world, drive anywhere, crash anything, dynamic blah blah), while in the other case does not spend resources to expand gameplay, keeps it closed and ramps up the pretties.
saying that these two are doing the exact same thing, is simply wrong.
personally, I will judge h2 with less forgiveness than dc (as getting to start with forza5 engine and assests IS a huge advantage), but that doesnt mean that I dont see or understand the differences between the two.
hopefully both games will be great, especially in what I care most for, playability.