The "great sword" was an evolution of the [longsword][1] (a two handed sword, no matter what Dungeons and Dragons tells us) that appears almost exclusively in Scotland and central Europe for a couple of centuries (after the Middle Ages!!) before dying out.

The greatsword was by no means a common weapon. Forget its effectiveness for a moment: metal has always been expensive, and quality swords were the weapon of nobility. A big sword would be even more expensive, and therefore only the wealthiest could afford such a weapon.

The wealthy also bought a little thing called "armor" (what we call "full plate" was also a Renaissance invention) that made a heavy shield unnecessary. [Indeed,][2]

>  It remained in use as a weapon of war intended for wielders wearing full plate armour  


However, any martial artist would laugh at "only range." Range is the deciding factor in a fight, all other things being equal. The greatsword remained a popular dueling weapon even after its effectiveness on the battlefield was eclipsed. The linked Wikipedia article goes into longsword fencing techniques in significant depth and should clarify the potency of this deadly weapon; what you call the "greatsword" is the same but more so. 

  [1]: https://en.m.wikipedia.org/wiki/Longsword
  [2]: https://en.m.wikipedia.org/wiki/Longsword#evolution