They are not tough to fight if you have invested well into your characters and levelled up their talents. Mitachurls are quite basic enemies you will encounter in the overworld while roaming different areas. So, they are easy to fight even if they are in a group with hilicurls. However, suppose you have low-level characters and don't have proper weapons or artifacts. In that case, you may need to reconsider your decision to fight. I recommend you invest in your characters. After that fighting, any enemy in the overworld will become a cakewalk.