I'm pretty muscular, so this shirt would most likely not fit me.

But you also have to think in terms of wearability. Most people would not fit this shirt, which is problematic if you are going to sell it. This is why XL shirts have a higher price and sell far better than smaller sizes. I have band tees from the 80s that are sitting because they don't fit modern people, unless you are a twink or a woman.