The converse argument that in its absence, muscle does not grow as well is not of the same logic, as you could make a person vitamin C deficient (scurvy), or even lysine deficient (corn only diet) and muscle will not grow properly, but vitamin C and lysine are not anabolic agents. It really is that simple. So, it very well may be that in the complete absence of estrogen muscle cannot grow properly. But estrogen is simply not an anabolic agent, no one would take it for muscle growth, and my hypothesis is that keeping it on the low end of normal will not hurt your muscle gains on AAS. This has been true for me and I monitor my blood levels religiously. In fact, I have had some of my strongest periods with my lifts when my estrogen has been on the lower side of normal, or right around normal.
Again, nothing personal.
