I think you've hit upon THE key distinction, here. Defining manhood shouldn't be done according to a "masculine"/"feminine" binary, and that's what we need to keep teaching differently to children.

Your historical example about the Spartans is very profound. Imagine an alternate universe where Spartan society still valued male brotherhood but Spartan women were truly equal to Spartan men in terms of achieving warrior status and serving in political leadership positions.

No one can stop you from being hopeless, but I want better for everyone who I encounter in my lifetime. I can't singlehandedly transform things (none of us can!), but I can still do my part.