Hmm. Maybe full-stack engineering doesn't need you to believe in it?
Though to be fair it probably does, because having your entire professional community believe you don't exist creates ridiculous amounts of frustration, anxiety and imposter syndrome.
I do (with skill levels ranging from competent to highly regarded):
* UI design
* Data architecture
* API design
* HTML/CSS/JS/React/GraphQL/etc
* Front-end accessibility (not the best, but I don't just do div/span soup and call it a day)
* Front-end performance (i'll spend weeks optimising the hell out of everything I see in browser devtools if given the chance)
* API performance (see previous).
I tend to draw the line at devops and sysadmin stuff, mainly because I don't find it interesting. But for everything listed, I do it because I enjoy it. And there plenty of aspects of engineering professionalism i'm not great at, which offsets the fact that I apparently have an impossible unicorn set of skills.
Honestly, I wish I didn't and was happy doing just a subset. But if I'm spending my time doing just design, I get frustrated that i'm not coding, and if I'm just coding i'll be dreaming of design. Also, the context-switching is hell. I wish my interests would let me specialise, but they don't.