For those commenting on the moat and such from the translations of the rewrite of this story I seem to recall this being in a canyon.....and the moat was wall to wall. I also don't recall him making a platform for archers with them instead being towards the front initially with some people with spears and what amounted to hooks on poles to push and pull goblins in and push them down. So yeah since they changed most the specifics of the plan and decided to equip people with oversized guando's they are calling spears, the only thing that's new here that doesn't seem weird is that he made a elevated platform for ranged fighters.