Should have re-balance those GW items to SCALING Mechanic like Lethality.
With nerf runes and balance runes... not everybody can access to goodies...
Therefore
: 35% to 15% (except full built should be 30% because one 35% LW would delete one armor item if stackable armor items.)
Why: average first armor = 75 therefore with 35% and it would be 48.75... (21.25 is a lot) PLUS don't forget bonus from champion and runes. Now imagine a champion with 150 armor bonus into 98 armor... that's a lot of numbers that reduces.
and 
Why: what a joke item for under 1000 gold... extremely strong item against sustain based champion.... Need to use scaling percent from 50% to 5%-50% (depending on level... like lethality mechanic)
and 
Why: No need to tune except % Pen.
GW.
Why: Same concept about use scaling percent from 50% to 5%-50% because it's usually to be first or second item. Very efficient item tho.