The skill system is really harsh on skill holders. Skill usage has limit and refreshes on the next day. Needed exp to level up seems to correspond to how high the INT is that is why INT3 seems to easily level up. And smartphone is needed to activate skills.

スキルの使用可能回数はたしかにシビアすぎる…

初めてダンジョンに入った後、何週間かレベル上げしている間に、レアガチャで貸し出せる使える武器が当ってないのでしょうか？

持久力、耐久力がないのは確かに問題。
解決できるでしょうか。