Which would be more like 400 AD to 1300 AD. That was when we literally had the Dark Ages, yet, many technologies continued to go forward.
Sure, they no longer had running water, indoor toilets, continuous hot baths, and other such things, but other areas went so far forward as to be unrecognizable to the civilizations of 400 AD.
A Cadre of Knights backed by Longbowmen or Crossbowmen would probably have wiped out an entire Roman Legion (if for no other reason than the Roman's weapons were weaker than the Armor of the Knights and would literally break before being able to hurt them, and the Bows would have a far greater range). That's even before we mention Rudimentary Canons and muskets that were beginning to be used.
Navalwise, the Ships had also advanced, and though they may have been more even, the way they operated was also different.
I can understand a Dark Age and losing some technology, but there would be other aspects that advanced that should have made the entire way they did things completely different and thus almost unrecognizeable at that point (of course, then that may make it so that it doesn't "Feel" like Star Trek to older audiences).