The primarily drug used in e-sports is Adderall. Adderall does not improve decision making, at least not directly. In fact if it's abused it can easily impair it. What Adderall does do is improve your energy, attention, and focus. Despite things like this sometimes being called "smart drugs", they do not actually make you smarter or in any way improve your cognitive abilities. But they can help you focus and pay attention, which is useful if your trying to study something difficult in a book, or if your trying to react to something more quickly.
If your paying close attention to things, then you might remember more details, which can indirectly help in decision making. But focus also helps you react to things much faster, which I think is the primary benefit. Which isn't to say that I think there is no thought involved in real times games, overall I agree that muscle memory is only part of the equation (albeit a big part).