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.
Yeah, that makes sense. I figure it could be useful for certain wizards who for whatever reason haven't hit 18 by the time they reach it. It's also good for when players want to play characters who it doesn't make sense for them to have really high ability scores but still want to see high intelligence dialogue options. But this is really just me musing.
For perspective, the headband of intellect is an "uncommon" magic item in the Dungeon Masters Handbook, which means that it is considered appropriate loot for lvl 1-4. A committed wizard will want a 20, so the headband isn't particularly useful beyond the early levels. I use it purely to boost INT skills in BG3, which is a fairly niche application. It can make eldritch knight or arcane trickster slightly more effective.
One big Caveat... in 5e the headband requires atunement to use, and you only get three of those. So once you get to higher levels almost everybody is going to want something better. The headband is a bit better in BG3, since the only opportunity cost is that you cannot put something else in the head slot.
