If you want to understand how physically demanding dancing as a profession can be, take a look at this article in Pointe Magazine. It points out that a study by the Occupational Information Network ranks dancers as the most physically demanding job in the US, based the level of strength, stamina, flexibility and coordination required.
A couple of years ago a doctor asked me what I did for exercise. I told her I took several 90-minute ballet classes a week. She responded by rolling her eyes and suggested I get "real exercise" instead. I no longer use that doctor, for this and several other reasons.
One could make the argument that an adult ballet class is largely an
anaerobic activity, meaning that it's bursts of intense activity with
periods of recovery rather than a continuous, longer-duration activity.
Think of the difference between a running a 100-meter sprint (anaerobic)
and walking briskly for 30 minutes (aerobic). Aerobic exercise is important to good health.
I'm not a professional dancer, and what I do compares to a professional dancer the way someone who enjoys casual bicycle rides compares to a Tour de France competitor. But that doesn't mean a ballet class such as I take isn't "real exercise".