On the topic of Eret, who do you think invented the traps? Improved on them? Figured out which ones work best for each dragon? Eret is clearly pretty clever, but I can see him figuring out how to use the tools he has in amazing ways rather than inventing them himself. Not to mention the size the forge must be to build those traps!
I think most of the traps were a slow evolution of experience and tweaking. I do headcanon that Eret didn’t start out on Dragons (only when he went south, away from a familiar life, and excelled at larger game), so he was raised with the passed on knowledge of traps, as well as animal behavior. What works, what won’t, which and where and all that.
So I imagine his dragon-trapping days started out of necessity, using traps he was familiar with. And as he encountered more people who fought dragons on a regular basis, he came into contact with those traps and methods, and it was sort of a melding of both experiences.
As he moved around, hitting up villages for trades and dragon-removal, he would speak with the blacksmiths (“I need something like this... but bigger.” “Can you make this weighted at all? It might help.”) and over the years improved the weapons he used.
In a way, I think he did have a tiny hand in the invention process. Mostly applying what he’d learned on the field worked and what didn’t and asking those skilled in engineering to construct something out of it.