stormbringer951
Against Eternity
The capabilities central to modern warfare force organizational and doctrinal evolution which leads you to something like modern warfare.
The alternative people are suggesting with tactical nuclear precognitive wizards and superpowered champions would also not result in a "medieval fantasy nation" because they would create drastically different conditions and thus result in drastically different societal and political organizations. Why would you have feudalism when your wizard only needs food enough for one person and a big library? You don't need the interlocking system of lesser nobles to create enough surplus, you just need to read more.
Yeah, the end result of a lot of these thought experiments doesn't really feel medieval but starts to approach a fantasy-themed army that can be described neatly in military technothriller weapon systems terms:
Charles Stross wrote a technothriller pastiche of magic vs tech, where the magic side is also described in very modern military terms. He has a lot of fun with how the baseline mechanical assumptions of their weapon systems and doctrine break down in combat against enemies from such very different technological paradigms: