Gender dysphoria is something completely different - the overwhelming sense that
one has been born into the wrong body, with the wrong anatomy and the wrong
physiology. Those of us who, whatever our occasional frustrations with the
expectations of society or our own biology, are nevertheless quite secure in the
gender identities with which we were born, can scarcely begin to understand how it
must be to grow up in the wrong body and then to go through the long and complex
process of adapting that body to match the real self."
I used to believe this too, and the reality is that this viewpoint is now really out of date - this hasn't been the mainstream view since around 2010. Firstly, the concept of 'born into the wrong body' has now been thoroughly debunked and disowned by trans activists - even Mermaids, the charity for supposed trans children, recently came out and said that no one is 'born in the wrong body' in any meaningful sense.
Secondly, your analysis relies very heavily on seeing transgenderism as a mental condition of which gender dysphoria is the main, central component. To be trans is to have crippling dysphoria and a sense that one's body is wrong. But again, this view is out of date and also regarded by many to be actively transphobic. There is a massive push by Stonewall and even the world health organisation to detach transness from gender dysphoria, so dysphoria is neither necessary nor sufficient for being trans. The current most popular idea is that being trans is nothing to do with a condition, or an illness, but is all about an identity - in some cases, a consciously chosen identity (see for example the work of Andrea Chu who admits they transitioned mostly for sexual purposes, but sees this as a bold, autonomous choice.)
Thirdly, even 'dysphoria' has changed. It used to be that gender dysphoria necessitated, in particular, surgery to alter the genitals. The dysphoria stemmed from being a woman with male parts, which was obviously deeply distressing, and so the male parts had to go. But now genital surgery is incredibly rare among trans people. Most trans women keep their penises and are perfectly happy with them - the current rhetoric is to say that the penis is a female body part, because it's attached to a female. Most gender confirming surgeries are now facial, or breast implants. In fact the Guardian last week published an article about facial feminisation surgery admitting that this should be now regarded as THE gender conforming surgery as it is increasingly becoming the most popular and only surgery that trans women have.
Ultimately, this entire story that there is a real womanly self trapped in a beastly male shell is now totally rejected by mainstream transactivism. Now they don't 'alter the body to match the real self'. `Rather, the real self is whatever they say it is and society has to adjust accordingly. So if I go on a dating site for women and I see a young man with stubble and some eyeliner, I must accept him as a woman if he says he's one.
I'd also like to push back a bit that women are 'secure' in our gender identities. Ultimately our gender identity is something that is externally imposed on us, that causes a great deal of strife and anxiety, and represses us from being our real selves. It's a big glib to say that we only 'occasionally' get frustrated with gendered expectations. I for one am deeply discontent with the 'gender identity' that has been thrust on me, and this is why I reject gender in all its forms. The solution is not for me to transition to try to simulate a man - the solution is to change society so women are seen as fully human as men. I'm not a fan of this constant rhetoric that trans people's struggles are the absolute apex of human suffering and women don't have it so bad because we are nevertheless "content" with our gender.