Its a nerf after that as well though, even then. It currently is 35% total armor, it is being changed to 40% bonus. Literally only champ negatively effected by this change for defense on the defending side is Thresh, who has his almost entire armor pool being based on bonus armor due to how his passive sets it. LW items still are at 40 AD, and the two unique passive routes on it still make you have to chose between stopping healing, or stopping health stacking. You don't get both out of it.
Also, now LW items ONLY work on ADCs, as AD casters who frequent mid lane have no use for bonus penetration compared to the total pen from current LW iteration, except in extreme situations where the entire enemy team is building/stacking armor.
And remember, if AD casters are having a worse time dealing with you, compared to now where they just laugh at you building armor at all, it is a one worse to the other being better case.