I dunno if we really want to get into crossing over into reality here, as rules/reality don't always mesh well.
A suit of armor was often a major investment, a high end big ticket product. (Think "Car") At bare minimum, it was a critical bit of life saving gear you'd care about.
Made by a master craftsman. . .and subjected to "test to destruction" on a regular basis, and unlike most situations in history, the rich person paying for it was often the one inside it avoiding getting shanked.
So, it evolved and developed quickly. . .despite what you see in movies.
Full articulated plate (real plate, not super heavy jousting armor) offers essentially full range of motion, weighs about as much as a modern soldier's load, and is properly distributed to spread the weight on shoulders and hips. . .I wouldn't think it'd be a good idea to swim in it (any more than I'd reccomend jumping in a river wearing a full modern load out either) but you could climb a rope, and move essentially unrestricted at essentially normal speed. . .(in segmented plate, Romans jogged 20 miles and then fought a battle). . . .the real life counter issues with closed armor tend to be that it doesn't breathe, so you bake in it, and between that and the weight it's exhausting to wear. . .after running or fighting in it for a couple hours, you would start to resemble the awkward, lumbering motions you see knights making in the movies (likely one of the reasons the Romans chose an "open" segmented plate, being infantry) but due to being exhausted, not restricted. If you wanted reality, armor would have minimal effects on motion and speed, and act as a multiplier of your rate of exhaustion, with the "closed" suits (8, 12, 16, 20) especially so. . .
Since most people ignore exhaustion, the maneuver/Qu mods end up being the balance factor, game wise. . .but if you get into what would be "realistic" you'd need to scrap pretty much all of the current logic.