I think you are simultaneously overestimating the scope of what Butler and other social constructivists claim and underestimating the scope of the meaning of what they actually claim.

I think you would profit the most when further engaging with these Ideas when focusing on this question you asked:

"Is this only to point out the fact that boundaries drawn and characteristics chosen in these distinctions are human-created (aka socially constructed?) Because this seems fairly self-evident, but I don't know what work it does."

Also think about the loop I tried to describe. By interacting with the world we also shape it and our influence is especially important for things close to us e.g. our own bodies, relationships, institutions, tools...