It certainly got lighter for the same protection. Overlapping rings are more metal for the same protection as a thin plate. Sure there was gun proof plate that was heavy, and tournament plate that was heavy as well. But actual battle plate as worn by many was in fact much lighter than the combination of mail, gambeson and coat of plates.
And I have seen no test proving that plate is better than the above combination. Sure as articulated plate, got more articulated, so the speak, there was less and less vulnerable points, and that should probably be worth a point more in armor value.
And yes an articulated plate is much more flexible as the combination mentioned, of course a simple mail shirt thrown over a tunic is both lighter and more flexible, but we are talking of an evolution, articulated plate replaced mail (including padding) under gambeson under a coat of plates. You try wearing 3 winter jackets and then bend your arm, see how 'flexible' that is.
If you are covered in metal, you are more or less invulnerable to edged attacks, turning swords into clubs.
One interesting thing you could do if you wanted more 'realistic' armor is increase armor values of metal armor by about 100% versus edged weapons, but and at the same time look at what the damage would be if it was blunt instead, then take the higher of the two as damage, more stuff to do, making combat take longer, but more 'realistic'. Depending on what rules you use for better success and/or combat hit roll modifers you can also let some armors have more or less vulnerable spots to hit. Also if the edged weapon penetrate armor, maybe reduce the armor value by one.
Notice I don't mention piercing/impaling damage types, since that's a whole kettle helm full of worms ;)
