Sex vs Gender - Which should we use?

This one is going to come out as more of a ramble I guess so if you are reading please bear with me.

Over the recent years we've had this cultural shift (or more the proverbial earthquake) regarding gender and gender identities so that we've gone from 2 genders to.....I forget how many its ridiculous which lends itself to a structural nightmare ultimately proving to be a failure in this day and age. To start with let's firstly define the difference between sex and gender

Sex - Biological 

Gender - Mental

So given the fact that biology is proven scientifically and therefore has clear parameters whereas Gender is a spectrum so vast that to pinpoint it correctly your chances are slim to none. To move on let's make another consideration who is this for? The individual or those around them. In my view this is for others, for example your name is yours but others use it more than you, it is how someone IDENTIFIES you. Now in social contact we use visual and auditory clues as creatures to tell us what we are dealing with, a gender cannot achieve this, why? Because gender is how one identifies oneself. For example I could go around identifying as a dragon overlord with thousands of minions and yet if someone were to physically look at me they would see a human male. Does that make them wrong? No, Does that make me wrong? No So where do we go from there? Well we go back to basics and IF my biology is male and I clearly show all the qualities (this refers to poorly attempted trans etc) then I should be identified as male. I'll give you an analogy

Say you work down the street and spot someone sporting a scruffy beard, long shaggy hair, poorly kept clothes and no jewelry or tech to see would you identify this person as rich? No you'd see them as poor and would treat them as such HOWEVER if said person was indeed very rich (or self-identifies as rich) then they aren't making the attempt to show this. The same is true of people like Riley Dennis, (if you don't know who that is you are probably still sane) they can claim they are female but with his deep vocal tone, the Adam's apple and lack of breasts it wouldn't be a surprise that people would consider them a male. What physical features qualify them as female? Long hair? Well many men in ancient times and now have long hair, or what about those women without long hair huh. Makeup? Look at the Celts, Egyptian pharaohs and similar who wore forms of paint on their face. The only things that can apply in any case are those biology has granted, the vocal tones, natural appearance etc as these prove this species has developed dimorphism.

Now you could argue there are a lot of women who look like men and a lot of women who look like women but ask yourself, how do they do this, Short hair? Makeup? Muscle? How about what are the key features, what things do we normally associate with men and women, make a list and tick off which feature belongs in which category (Chromosomes, Hormonoes, Genitals) guaranteed you'll find they are more one sex or the other and then you have your identification and that's if you want to drag this out.

Again sorry for the ramble, in conclusion, I think we should scrap gender and go with biology a.k.a sex as the only identifier in society between males and females.