But also pretty anachronical as a tech being researched after 500 BC, I wonder why that even made it in the game 

What's cool about ChatGPT is that it lists sources for its answers:  I know some peoples' cognition has been undermined by overreliance on LLMs, but I'm learning so much:      

I've done that with the hack armor techs in the Forge for the Han just now.  I won't do it for every tech,  but where the differences make sense I will. For instance, the "Wooden Shields" tech icon seems pretty applicable to every civ. 

I like the idea of garrisoning and having a long wait time to get the resources. You can get more than destroying them, but it takes longer

Just checked, and it doesn't seem so. I think you are confusing it with Self-Destroy for a building that has not been completely built yet. In that case I think the resources recouped are according to the unbuilt fraction, which makes perfect sense if one thinks of it as the resources having been set apart beforehand for construction, the resources already used being lost since Self-Destruct is (when not just a cancellation of plans) a fast destructive way to get rid of stuff (making things collapse or setting them on fire, maybe some graphics representing that would be nice, not so much for the suicide of organic units though...), quite different from salvaging.