Stupid idea: Defense stats converting to other defense stats.
So random idea just now. What if there was an ability (champion passive, mastery, or item) that converted a % of your max/bonus health into armor and MR or vice versa?
It's probably a bad idea, but imo it seems better to balance than converse defensive stats into offensive stats. Plus we already have someone that converts offensive stats into other offensive stats. Jhin and his book of a passive.