Well, making 1-dimensional, simplified* definitions out of something that's so multi-faceted is only gonna hurt yourself in confusion in the long run and really isn't that helpful, given the context
Who are we trying to convince, the characters, the author, or ourselves?
sure, there are biological sexes, and then there's gender - and no, it's not 69 genders or attack helicopter; gender is gender, and it's more of an expression, a performance, an alignment or whatever you choose to call it: and yes, most of the times, gender is not entirely separate from sex
And depending on what kind of question you're trying to answer and for whatever purpose, labels can be important or they're not
Questioning is good, but at the end of the day, only you can know for sure, there's no lying to yourself
But sure, if the simple distinction of male - penis/testes and female-vagina/ovaries is enough for you, then it is enough, end of discussion
Just don't be surprised when you find out the actual world is much more complex and diverse than that.