Dear god, folks the arc is fine, its at a moderate length, its exploring the characters and their backstories, its fine for a narrative to take its time and flesh out its characters, you can't get pay off without set up
If you are hate reading this, you have my permission to stop now and find...
So, for folks not aware, this is the same author of Buster Keel. Buster Keel, for all intents and purposes, was clearly, a Fairy Tail clone. But as time went on, it became steadily more its own thing. And more importantly, it had real, genuine heart to it.
I am genuinely feeling that here too...
Considering he almost fell for the room of cursed artifacts, and was surprised in the first place by Iruma, he likely came up with the plan on the fly. 50/50 chance he did this expecting Iruma to flounder under pressure and use the distraction to get to the vault.
To be fair, the bow creation skill is incredibly rare
Not like the author is working backwards to justify rare, but as in Bachiko famously has had few if any students besides Iruma, and fewer still who passed her training. Then they have to be talented enough to mimic her. The likely only folks...