A person that wears full plate would move rather slowly. A full plate class would be more of a defensive counter attacker. Unless on horseback. Alone a full plate wearer would be rather vulnerable, but in group settings they support rather nicely.
That is already what is happening in cRPG: very vulnerable alone against multiple opponents (low running speed, poor footwork), moderate duelling potential (slower average weapon speed), powerful finisher in a group (very high damage output), cannot pursue an opponent that does not wish to fight (need to work with teammates to close off way of retreat).
Then damage reduction (with the armor rating, enhanced by iron flesh) extend the normal lifetime of the player, coupled with blocking and footwork, you are almost invulnerable except when completely overwhelmed or consistently making mistakes, making the full plate class a very user friendly class (but high to upkeep) when you are aware of the ebbs and flow of the battleground and always remain close at hand to your team even if you are only an average player.
Then, like Oberyn said, if you wanted to apply realism to plate armor, you would have problems with the current way of how damage is applied to armor and the weapon type used to maim your opponent. Only blunt force would damage a wearer of plate armor (except if weak points were added).
Still, the way damage formulae are applied in cRPG, if you wear plate armor (around and above 60 armor rating), some cut weapons will glance away easily (recent change in weight of made that happen less often) or do little damage, "simulating" the fact that the weapon didnt CUT but applied the BLUNT FORCE trauma of the strike to the wearer instead.
(or at least do enough blunt damage through it to the person underneath)
That way we can say that, even if unintended, plate is already pretty tough and realistic
