how is the knowledge domain less themed than tempest? I'm not saying you're wrong, rather that I don't understand...
I'm saying the subclass is more universally useful regardless of the type of cleric you play:
1. Spells: Command & Identify (both useful)
2. Two skill proficiencies (with expertise) from Arcana, History, Nature, or Religion. Arcana and Nature are the most useful IME, but Religion can certainly come in handy. I've even seen History help out in games.
3. Channel Divinity: Proficiency in any skill or tool for 10 minutes. Very handy IME due to times when no one has a skill that is needed or at least your Cleric doesn't.
4. Channel Divinity: Read Thoughts with possible Suggestion use. I've seen this used effectively in social and "exploration" situations, it is even useful in combat.
5. Potent Cantrips (no brainer for combat)
6. Visions of the Past - knowledge is power IMO, but I've never had or seen a cleric reach this level. I can see times when this could be useful, but haven't yet.
So, this subclass is useful in all the pillars IME. It is not "great" in specific ways like some others, but generically good all around.
By comparison, Tempest is great for combat, and the final feature more useful than Knowledge's for both combat and exploration in general, but the other features for Tempest aren't as universally useful.