Mind control magic would indeed be a huge deal under isekai circumstances. In a game, it's not such a big deal because even if mind controlled, NPCs in a game can only do so much. Basically they aren't hostile anymore or will perform a single pre-scripted action demanded by the story. Skyrim, for example, has a number of mind control spells and powers, but they are most certainly not game-breaking elements. But those same powers in a living world would be a big asset or problem, depending on whose side you are on.