While this idea has been passed around a lot,mostly with negative votes,i would still like to post it up,though i understand rylais,zhonya's and rod of ages give health and armor,they still are not as efficient as warmogs on stacking health,you may argue a mage should not have much as they are burst,i agree,but my point is to stress on tanks like alistar,blitz,singed and amumu, most cases they either get to chose between high damage or extreme tankiness,while i do not deny,they have good amounts of health innate,it still would not suffice for a tank role when built ap,and when built fully tanky,they tend to loose out on damage,which an ad tank may possess,the item may seem op but we have to understand that no item is op,it is all the matter of ratios to be exact,so by providing a percentage of health as ap but rather a small percentage,an ap atma can be created which can be quite beneficial.
please do not down vote,tell me your opinions in comments