There is no lock in, there are merely incompatibilities. You can install sudo, but by default there is devel-su which is pretty much the same thing. You can install rpms and if you don't like pkcon you can install zypper as package manager. As long as you stay within the terminal emulator things tend to work.

There is a misunderstanding that desktop programs would be such a great boon for a mobile phone. But mobile phones suck with desktop UI. You need a mobile UI for it to make sense and that is exactly where incompatibilities are coming from.

I installed a community port of the qt6 based KDE plasma browser Angelfish for example and it is running just fine on Sailfish OS.

They just have their own format using their owm SailfishOS-specific UI libraries. Their apps don't work elsewhere without patching, there's no Flatpak and they only have SailfishOS apps in the repo.

Sure, you can write your own apps, but I prefer using what's already there.