Mana burn would be pretty broken, but a manasteal would be nice on some champs. Just like life steal it would just return a percentage of damage dealt. --- There are 10 types of people in the world: those that know binary and those that don't.
Wit's end had mana burn and it was considered pretty useless.
It was good against very high mana cost mages--Anivia is the only one that comes to mind right now. It was also good mid game against supports and ADCs who still relied on spell burst like Tristana and Graves if he were around at that time. It was a situational item--you obviously don't get it against Kat or Akali, but that didn't make it useless.
They removed the "mana burn" item for good reason. Doubt it will ever come back.
Old Wit's End had mana burn. People QQ'd too much about it being useless against manaless champs. Such a dumb argument. Not everything is good against everyone.
People QQ'd because people that relied on skills, but didn't want to buy items early (e.g. rammus) were getting completely wrecked by this, whereas manaless champs are unaffected. So you are half correct. --- PSN: boozinator23 Steam/LoL/Minecraft: Funkedelike