Is there any point in taking Myostat while on a calorie restricted diet?
I don’t see any reason why not. It hopefully increases the conversion of satellite cells into muscle cells, so even if you aren’t able to hypertrophy the resultant tissue (due to diet), you will still be getting extra tissue that you can hypertrophy later.
Also, see the thread about gaining muscle and losing fat at the same time… because if you can do that, then myostat would definitely assist you.