As I have said before in my own posts, the solution to this is really to tone down the amount of Lethality granted by items, and to build a Lethality boost and/or steroid into the kits of those champions who are meant to use Lethality. For example, a champion could gain a bonus 50% Lethality, so if they have 10 from an item, they would have 15 Lethality total.
This way Lethality is still minimally effective on champions who are not really designed to use it, but the option is still available to them. Meanwhile those champions who are designed to use it have the ability to do so to the full effect, and can be balanced based on the stats in their own kits respectively.