While I like Stefan Struve I think that was a bigger upset in September than people thought, especially since it was a tko.
If not Browne than someone like winner of Jordan-Russow, Mitrione, or even Cheick Kongo even though he's coming off a win. Stipe wins any 4 of those fights imo.
Also it hasn't been that long and especially not longer than Overeem. When Overeem fights in Feb it would be a year and more than a month since he fought. Let's say Stipe fights at latest in the summer which would be awhile, that would be less than a year.