Also, weight is not the only problematic aspect to armour and such.
For all items, there is also bulk.
And for armour, most armour has some restricting aspect on movement.
For example ...
Imagine a full suit of plate mail - it consists of segments of various sizes, held together by joints, straps and the like.
While the articulated aspect of such armour is designed to allow movement, it does not allow complete, unlimited, unrestricted movement.
Even if it weighed virtually nothing, the armour does impose some limitations on how the wear can move the various parts of his body.
Imagine a 1 meter by 1/2 meter by 1/2 meter box that weighs less than a dagger or large knife.
Obviously, the dagger or large knife would be easier to handle and move around than that 'box of air'.
That is, almost as much as weight, the actual size of an object (i.e. how bulky it is) has a large effect on easy or difficult it is to move or carry around.
DonMoody