Weapon shop isn't useless it's just a cheap way to get the starters for most of the weapons, from there you can advance each of them.
But at the beginning, it's best to use your sword and shield and have some nice armor.
Thinking back I remember killing Great Jaggi with the basic sword and shield I was fixated on shield bashing it to death until it died from it.
I'm Unamerica and you can too.
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