Why perpetuate such myths? Harness is well distributed weight, and is less than 2/3 the assault load of a modern infantryman.
When well designed, correctly sized and worn it doesn’t prevent any of the motions of the european martial tradition (but because “harness fighting” was usually practiced against armoured opponents, there is a difference in combat style that uses a reduced requirement for parrying and a change in the offensive needs from slicing and hewing cuts, and thrusts from longpoint, and to stunning blows from the pommel and seeking thrusts with a ‘stiffer’ shortened blade tip in half-swording styles).
Poor quality of design and fit of much “practical” modern off the shelf armour (including no calf shaping on leg harness, poor suspension of leg harness, overlong breast plates) are a thing that inhibits effectiveness, but they are not features of the real armour.