I got fat as a child because I used binge eating to cope with a series of traumatic experiences. This poisoned me on a foundational level and kept me from every developing a personality outside of being the funny, self-deprecating fat guy, or someone with poor impulse control and zero discipline.
I lost 150+ lbs and once it started becoming a regular occurrence for me not to be the heaviest person in every room I walked into, I had an identity crisis of sorts. I started losing weight and realized that there was nothing else about me, nothing serious at my core.
All of my interests, friends, and perception of myself were heavily entangled with me being fat or with the C-PTSD that made and kept me fat. I've changed nearly everything about me, diet, hobbies, mindset, and seriously everything. I'm a completely different person because of the physical and mental process of losing weight in a healthy, sustainable way.
The more I become my own person on my own terms and get to actually grow in healthy and positive ways, the more obvious it is that I was, in every sense, a big fat guy and very little else.
I can only speak of my own experience though, and I know that it is not universal. Everyone should be able to define themselves how they want.
For me it seems like when people see themselves as just the fat guy it makes he harder to lose weight. It makes it harder to do so many things because they connect with that idea of being the fat guy. ( I got have lost some pounds) not on your level so I am also speaking for my journey and not trying to take thing away from yours . It is odd that we see the same thing and come out with different points of view. (not suggesting you are wrong in any way).