Melee ADCs and lifesteal

After playing League for over a year, I can say that this class of champions is problematic.

Champions such as Fiora, Tryndamere, Yasuo, Master Yi - they become completely unstoppable when ahead. Things are fine and even in the early game before they have a lead, but when they snag a couple kills, it gets really unfair for the other team.

Lifesteal - The core reason these champions aren't fair. They can jump from enemy to enemy being at full health if they build enough of this stat. Ever seen a Riven take on three people at once? She probably had Ravenous Hydra and Bloodthirster and was healing 300 health on each auto. You should be able to build tons of damage when you get a lead. You earn it when you get a lead. But what you shouldn't earn is the ability to heal through all damage unless it instagibs you.

Just CC them - This is a valid solution, but it doesn't work at lower elo, because the carries have to follow up the tanks with their damage to finish the deal. This coordination is hard for newer players, and the carries can't get close to half of the champions in this class. If I'm playing say, Varus, I can't afford to go anywhere near that fed Fiora. I can't be in auto attack range or else I'll die. But the tank can't kill them alone. They need my damage. What do I do?

Everyone remembers getting pubstomped by some Master Yi or Tryndamere in their early days. And they shouldn't. They should remember the smart players, not those who get away with building six BTs and right clicking their way through the enemy base.

So what can be done to balance these champs? My suggestion is limiting them to building only one lifesteal item, similar to how gold gen items work.