If you *really* want to start a fight with a medieval historian, bring up the idea of the dark ages and be prepared for an hours long discussion. :-) Instead, the academic divisions are early medieval, high medieval, and late medieval for reasons which a medieval historian is better qualified to comment on (I'm a Renaissance/Early Modern Historian).

One of the first references to the "dark ages" is in the work of the Italian proto-humanist Petrarch who was a bit of a showman and wanted to distinguish himself. For more on this look at: Mommsen, Theodore E. "Petrarch's conception of the'Dark Ages'." Speculum 17, no. 2 (1942): 226-242.

Renaissance Humanists adopted the idea because they wanted to claim they were heirs to the Roman tradition and continue to distinguish themselves for many reasons, including the self-promotion which led to noble patronage and positions at court or other types of employment. There are all sorts of other complicated reasons they made this demarcation including a growing divide between religious and secular philosophy.

While I don't think anyone would argue that the Renaissance saw a great deal of technological, intellectual, and scientific advancement, comparing the year 1000 to 1500 is not as fruitful as understanding that historical developments ares not always teleological and can take a long time. Making a sharp division between medieval and Renaissance isn't particularly helpful.

Not to mention lots of important and game-changing advancements took place in the medieval period, including but not limited to:

--Banking

--The University

--A shift from Latin the Vernacular which opened up education

--Notaries and notarial culture

For more on this topic, start with John H. Arnold's What is Medieval History? and Barbara Rosenwein's A Short History of the Middle Ages