I'm not sure if there's varying levels of severity?

There are, but the big thing about the impact on fertility is A) where the scar tissue is and B) how soon they catch it. Endometriosis basically means you have tissue that should be inside your uterus in other parts of your body. It can tangle up on the ovaries, the outside of the uterus, the fallopian tubes--basically it gunks up the works and can make you infertile. While mine was caught later than I would have liked, at age 29, my scar tissue was almost all built up on the wall of my abdomen, leaving my reproductive organs relatively unscathed except for some torsion of one ovary (that my OB managed to save in surgery). So I got lucky--the location led to a lot of lower back and GI pain, but spared my fertility. I then got on continuous high dose BC and stayed on it for more than 3 years until I decided to try for a baby. After I started the pills and stopped getting periods, everything was better. It was like a miracle. I'm lucky--some women need multiple surgeries, and Lupron, and heavy duty opioid painkillers.

she's extra angry that just about every 'lady problem' that walks through ER is dismissed is "not that bad"

Oh, hell yeah. In fact, the doctor on call in the ER basically rolled her eyes at me and wrote me off--she said I didn't need surgery, but 72 hours later I was in surgery after I followed up with my OB and she say my ultrasound. My first OB ever when I was 17 told me "this pain should get better by the time you have your first child." In my early 20s, another doctor told me "this is just something women have to deal with." Finally I found my wonderful OB, who took me seriously.

Unfortunately, there was a time when hysterectomies were handed out as a solution when they weren't entirely necessary (especially when a woman is of "advanced maternal age"), but now it seems like doctors are moving away from that.

I have no idea if my previous pain experience made it easier for me, but I totally agree with you that many women are too often left in the dark about their own bodies and not taken seriously by their doctors.

I think the same can be said about childbirth, actually. Unless you read up about it and educate yourself in advance, no one tells you about different types of fetal monitoring, or that they will often push for an episiotomy to speed up delivery even if it's not necessary (which actually happened to me, but I declined it and everything worked out fine), or that they might have to break your water, or that they're going to knead the heck out of your belly after the baby comes out and it will hurt a lot, or even that there are different stages of labor. I know no one really needs a class in order to deliver a baby, but I'm very glad I took a class.