Earlier quoted context omitted.
I was under the impression aerobic exercise has benefits for the heart, lungs, and circulation, at least? Can you elaborate on the "barely anything" bit?
Classes are either not long enough or not enough intensity (look up HIIT) for good benefits (you will get some initially but will quickly stall).
If you view fitness as a means to an end (health/long life) then you've got to realize there are diminishing returns. There have been many studies showing the diminishing returns kick in very quickly (http://well.blogs.nytimes.com/2014/07/30/running-just-5-minu...).
If you want to be an elite athlete that's fine, but you should at least acknowledge it's its own reward and not claim it's about health.