I'm just going to answer number 4 (oh, and tell you that my first ever experience of MM romantic fiction was also fanfiction, though from my favourite game as a teenager Final Fantasty 8, before that I just had to imagine, and wish for a better internet connection)
I barely ever know/remember/bother to find out the gender/sexuality of any author published/self-pub/not-pub I am reading. This is not deliberate, I've just never found it useful information.
Terry Pratchett (may he be forever happy in whatever heaven Death took him to) was a straight white guy, and yet every character he wrote, from teenager shepherdess witch to sly con-man who takes over the post office, was believable to me.
I am currently reading A Closed and Common Orbit (Becky Chambers) which is about a space ship AI housed into a body (which happens to be roughly female), and she is believable too.
I like to think my demons are as believable as my cowboys, and hopefully as good as my female characters, but I'm not a demon, and I've never lived in Texas (more's the pity).
Anyone can write anything, as long as they work at it and have a good idea to start with. And I don't see why anyone should ever mind.
Also, I’ll agree with you about some traditional female MCs (having fought my way through books "recommended" by my mother), and I don't know any women like that! Who are these skinny, superficial, fashion obsessed, easily walked over individuals hell bent on being miserable?