He really blast it down…
XD…

If you reread the chapters after the enter the town, it is implied that Rona was the one behind those adventurers. She was going to wait till the last moment to save Shion because she wanted to scare her enough that she would give up being an adventurer. That’s why Fritz keeps harassing their party. Rona is behind all the Shion harassment. I imagine her orders are to
1. Keep Shion safe
2. Make her return to the king through manipulation and not force

As for Rona herself, it’s hard to tell what she would do if not bound by her duties/orders.

Imagine using a Spirit Bomb to defeat Majin Buu (or whoever) and destroying half the earth in the process. That’s what Renya’s mindset was. Essentially, at that point, he wasn’t confident that he could resolve the situation without using an over-the-top magic because he still lacked competence in using magic. It’s a matter of optimal efficiency versus unbridled power — a sniper is usually more useful during combat than some guy running around with a machine gun.while having no understanding of the concept of friendly fire. Going full OP mode against every opponent isn’t something that a competent magic-user would be doing.

It more than likely it is one of those martiral arts thing that he should not over confident with himself and he needs to do more training for the next battle. Since he had the so called terrain advantage it most likely won’t work it the next battle. Or just he thinks like the Samurai’s in “Samurai 7” that never no point in celebrating they won the battle since there will be another one.

I know, right…? Well, that’s the problem with Renya’s messed up way of thinking. He wanted another effect, it failed, so he considers himself him no good. Total lack of common sense. xD

Spirits of the wind heed my call!