Mick P. said:
I am pretty sure that 20kg is not full plate. It's just plate plate. In full plate you are a tank. You are doing good if you can stay on your horse (that you were lifted up onto with a crane)
That's a fallacy even if you ignored the evidence against your argument and look at it logically.
Plate that would be so heavy that required lifting onto a horse is utterly and totally impractical in any field of battle. How would they be able to move such a crane to the battlefield? How long would it take to set up the system to mount the heavy cavalry? Not to mention if you were knocked off your horse you would be useless in a fight.
People seem to assume, for some reason, that those in the medieval era and early Renaissance were stupid and would come up with things that impractical. They were not stupid, their armour was designed for easy mounting and dismounting, and to be able to fight in no matter how the battlefield changed.
Plate was a great, mobile piece of armor that gave great advantages to those that could afford it. It only died out because of advances in gunpowder weapons more easily able to pierce plate, the rise of the pike formation that made heavy cavalry obsolete, and the re-introduction of formalized armies during and after the 100 year war, giving rise to the superiority of firearms wielding infantry. Even then, that type of body armor wasn't entirely abandoned until the late 17th century, with remnants of it lingering on even into world war one.
Plate disappeared not because it was so big and heavy it was stupid, but because advances made elsewhere rendered it obsolete.