⚔️Serberia

There are several nuances here:
1) Alessia's mana is not infinite, and it will only last for five casts. There are potions, but they are not cheap and only provide one extra cast.
2) In both battles with the generic bandits, the rune would not have given you anything at all – both battles ended before the effect of the spell could take place.
3) In the battle with the slum boss, the rune, again, did not have a significant impact on the outcome of the battle – it did not deal any damage and only served as a scarecrow for Isabella, forcing her to use one (potentially two) of her actions to move. This is not useless, as it saved Veserod's life, but it is not something that decides battles on its own or allows you to clear encounters without engaging in combat.
4) I expect the sewers to have an architecture similar to the "Princess" base, i.e., many small rooms and narrow, branching tunnels. I don't think I need to say that this does not encourage the use of such spells.