I'm just gonna share my personal story as a response to OP's question, and declare how I identify myself now and how I've identified in the past. I make no judgements of others. I'm on topic. Just wanted to clarify that first, seeing as this thread went in directions, and me reviving it might... I dunno, stir a pot, or something.
I began my detransition very recently, just almost a month ago, so this might be too soon for me to make a clear statement about how genuine or right this is for me, but, as far as I know for now... I'm doing a total 180 turn from having lived as a mostly masculine male (how I saw myself) back to a very feminine female (my birth sex, and how I currently see my gender). I don't consider myself to be transgender/transsexual and/or non-binary, but I used to think I was a binary trans man. I now consider myself to be a binary cis woman who made a (huge) mistake.
As far as I've heard around, it is rare for transitioning people to realise they're not actually trans at all and want to undo everything and live entirely as their birth sex again. Turns out I'm one of those few people. I got the short straw, I guess.
How happy I am about it though... well that's a tough question to answer but I'll try my best. There are two sides to it, the one in which I'm terribly upset over the more or less permanent physical changes I've done to my body which I now regret horribly - and the one in which I feel a genuine connection to my remaining birth sex traits and to being a woman like I never have before. I feel happy to be a woman though, and I look forward to getting my body restored again and to live the rest of my life in a female gender role. I don't like absolutely everything that's societally connected to the female gender role, but then I don't think any girl does.
I lived as a man for almost a decade, 9 years, and I passed very well for the last 4 of those. I looked good, I was attractive to others and never had trouble finding company. I liked it, in some ways, but it wasn't the real me. In fleeting moments I had doubts and missed being a woman. I dressed up in drag a few times to test myself and it frightened me. I tried hard to push those doubts away and just carry on as a man. I told myself it was what I truly wanted and I believed in my own lies.
It wasn't until last year when I planned on getting SRS that my subconscious started fighting back against me. I got as far as to schedule with a surgeon and ended up on his waiting list, when I got a gut feeling so strong that I felt it almost knocking me over from within. When I listened to it I got aware of that I really love my vagina and don't want for it to be a dick there at all. I had thought it was the reverse, but then I suddenly aligned with my primary sex characteristic trait. That was my first real sign that maybe I'm not actually trans, despite everything I had believed up until that point. The lies I had been telling myself had begun to unravel. Eventually I dared to dig into my mind, and I found out it was all because of my past traumas that I thought I was a trans guy. When that dawned upon me, I didn't want to escape the truth anymore. I embraced it, although it was very painful and facing probably my biggest fear. Now I don't want to be a man anymore, and I miss my true womanly self that I tossed away.
My case is similar to that of the transphobic Walt Heyer that you mentioned, as I also have DID or some variant of it and went through a lot of trauma in my past that messed with my mind and relationship to my body. The difference is I did not become transphobic upon my detransition. The sexual abuse I went through as a child and teen made me target my gendered physical traits as something to hate and be grossed out by. That seemed very similar to gender dysphoria, but it wasn't that. I was never trans to begin with, I just convinced myself that I was. Nowadays I've come very far in my healing, accepting and loving myself. I still carry that pain from the traumas, but I don't hate myself for being female anymore. My gender was never the real issue but it was what I targetted and attacked. I used to consider myself totally male before, but now I know I'm totally female and I love being a woman. I love being feminine, wearing makeup and dresses, etc. For me it was a mistake to transition in the first place. I should not have done it. So yeah, I'd say I am truly detransitioning.
As for physical changes I want to try my best to reverse everything or what can reasonably be reversed. But that will be a long journey that I haven't even started yet. Most of all I'm looking forward to getting new breasts, and I want to go big. But will also do voice training and beard/body hair removal, and get my hormone levels back to healthy female range again.
I present very similarly to how I did pre-transition now, but a little less like a teen girl and a little more like the almost 30 years old woman I am now. Because it's been so long since then, it does feel rather strange. Like I've suddenly woken up from a mist and aged 10 years over night and I'm not fully grasping it. But it does also feel very right within myself and just the way I like it. Detransitioning is a relief for me. So yeah, some people do truly detransition, but I don't think it's common. Percentage I've no idea, but probably less than 1% of those who've done a gender transition go from one binary to the other and then back again, if I can pull an unfounded guesstimation out of my rear-end.