Also it's not done here, but something I think a lot of people don't realize is that great swords are often not sharpened all the way down near the hilt. Or even if they are, you can still grip them with gloves.
So a lot of greatsword techniques involve holding them up on the blade with one hand as a fulcrum and using the back hand on the hilt as a lever arm, turning the whole thing into a short spear. You wouldn't swing it in ways that create a heavy impact on the hand holding the blade, but a greatsword can be wielded very flexibly like that.
The main reason greatswords were rare wasn't because they were some bruiser of a weapon which only a few people wield. Held properly they're pretty easy to maneuver. It was for a simple reason:
Swords suck and they're expensive.
The way the greatsword is effective up there? Yeah a polearm can do that better, for cheaper. (Not 5 m long phalanx polearms, I'm talking about stuff closer to 2 m). There is basically no circumstance in which you want to fight a polearm with a sword, except very specific close quarters circumstances where there's a lot of twists and turns.
The entire reason you want a sword is that they're easier to carry. That's it. That's the whole reason. It's easier to carry a sword without having to use your hands. That's why they're known as sidearms. Because you can carry them on your hip.
If you had the money to burn for an expensive status symbol just for the privilege of being constantly armed even off the battlefield, or as a backup weapon if your polearm got broken, you bought a sword. But that's it that's basically the entire reason you get a sword, they are an inferior weapon in terms of actual combat capability, they're just more portable.
Which makes greatswords kind of weird, because you will notice they are not very portable! And they have even more steel and even more cutting edge to add to the already substantial expense of a sword!
So their main use case is cultural, in cultures of sword fighting which develop around wealthy military classes which are likely to have swords. The constant presence of swords in daily life and the way they act as a distinguisher between military aristocracy and peasant levies create an outsized emphasis on swords even though they're objectively a worse weapon. Which is how you get showmanship duels and tournaments focusing just as much or even more on swordplay then polearm combat.
And in that context a greatsword brings some of the advantages of a polearm while still being culturally recognized as a sword. So it might be culturally acceptable to duel with a greatsword, and advantageous to do so, even though it doesn't have any of the benefits of a more normal sword.
It's a cultural thing, in other words. It's all this big cultural artifice around exhibition weaponry even moreso than it's about actual practical battlefield uses. (Which isn't to say that people wouldn't use it on the battlefield, it was just very rare).
Also it's big and phallic and that definitely mattered.
