I've never really used this item for long since I don't tend to kill the ogres, but the one defence that might apply here is that with the item, you can't actually increase your intelligence beyond that, and it stops being useful once you go over 18. So you'll never get to hit a +5 ability modifier. Is that valid? Does it make sense?
It seems counter-intuitive to me that a "Headband of Intellect" will never be useful for an Intelligence class.
It's best for a min-maxed hybrid spellcaster like an Arcane Trickster or Eldritch Knight who can dump Int to 8, but will potentially greatly benefit from 17-18 Int. Encouraging min-maxing and dump statting doesn't seem like a good way to design items.
