Temple rewards seem underwhelming, how do I improve this?

You are missing golems. Which increases the effect of some rooms multiplicative. Also Corruption Chambers are op to add additional modifiers.

• You have a lot of normal garrisons, which don't really do anything for you
• Same for armories. They only increase normal monster effectiveness, which isn't doing much since most of your drops come from rare monsters
• You have 0 Golem Works, which increases the effectiveness of a lot of the rooms you use, but most importantly the legion barracks, where you get your rare monsters from
• You have 1 Corruption Chamber, which is what gives your rare monsters additional modifiers, which really amps up your drops. A normal non-tech temple should have 2-3.
• You have a lot of holes in your temple, meaning you're missing out on a lot of potential rooms. Min-maxed temples usually only have 3 missing slots, and you have 15 open slots. That's a LOT of rooms that would contain lots of rare monsters + more temple modifiers.

Build a new one and use a guide, your temple is not even worth running.