I think the difficulty is you don't want to nerf what makes the item great but create a bit of a trade off by buying it. So bluestone for example. Great clear, great damage over time. But it's meant to be a item that makes you more at risk of ganks etc while keeping that damage, it's (meant to be) a high risk aggressive starter item. 20hp5, immediately at the start of the game doesn't make it risky at all. Especially if you're a god like Tyr or Guan who has self heal. So that's what you'd target for balancing.