Everything happens on my terms. The phone never tries to grab my attention unless I explicitly make it so. All the things I use are FLOSS. I can patch anything I want down to the kernel and bootloader, often on the phone itself (see
https://news.ycombinator.com/item?id=49191008). The OS is managed the exact same way the OS on my PC is and all my skills and knowledge directly transfer over, so I can script it or write applications the exact same way I did on PCs for decades. No "side-loading" shenanigans whatsoever. I can use any browser I want with any extensions I want. I've even used it at a game jam once - plugged a screen, keyboard and mouse in and made a game with the same tools I would have used on a PC (QtCreator, Allegro, GIMP, Inkscape, Audacity, LMMS) and cross-compiled it to Windows and macOS right from the phone using the exact same tools and workflow as usual.
I could probably go on and on. It feels like my little personal pocket computer rather than an appliance that someone lets me play with on their terms.
BTW. Funny how it can go from "it can't possibly replace Android/iOS" to "how is that different from Android/iOS?" :)