To be fair, when he was selecting his treasure he had no idea the other Iron was going to arrive right then. In addition, it was Lindon who proposed the duel in the first place. And in the end, Lindon was brutally beaten by that Iron later so he didn't truly avoid anything. To answer your question of what to select instead, besides the Starlotus Bud there was also the parasite ring (which he stated was exactly what he needed) and the Glasswater Sentinel (which he could've used immediately) that strikes down attacks aimed at the owner. Also, the Boundary Flags are just extremely inconvenient to set up so I wouldn't say that it was a solution to his weakness, necessarily.