This question poses a bit of a quandry for me as a yoga teacher.
Perhaps others can navigate it more skillfully.
My challenge here is that I don’t define yoga as a weight loss program. Yes there can be changes in the physical body and yes those changes can be sliming and toning, but there are plenty of robust yoga practitioners with very lovely, meaningful practices.
Yoga, to me, creates change in the external body from the inside out. It balances self-worth, self-esteem, and hieghtens awarenss (which allows the practitioner to examine their eating habits more deeply).
A tone body is not the end result. Rather it’s a result more toward the beginning or middle of the practice (as a whole). While I don’t think there’s an “end result” at all a more accurate “end” would be evolving.
And of course there’s a physical component to that.
More to your question though…do your aerobics if it fits for you. Your yoga practice may grow. It may grow to the point where your perception is that it is NOT a substitute for cycling, jogging, step, tai bo, or the like but a practice unique unto itself.