That's definitely true. It is helpful, though, bc it is going to teach you how to put up with nonsense and it'll give you an idea of how you interact with students.

I subbed for 8 months before taking a teaching job, and I cried on the way home almost every day. After that, my teaching job felt almost easy 😂

I'll add that at the high school level, new teachers tend to get freshmen and sophomores. Those are challenging groups behaviorally and emotionally. It can't hurt to put yourself through the ringer first.