First, you don’t have full control of your system. Your system is running an unknown amount of code as binary firmware blobs even if you’re using a completely open source kernel. Hopefully you’re compiling every package yourself and not using pre-compiled binaries from your distribution’s repositories.
Second, immutable distros are primarily a distribution and update mechanism that vastly improves the current model of running X number of package updates and scriplets on every machine and hoping it works. There’s nothing that stops you from remounting a filesystem as rw at least on any of the distributions that I know of. There’s also plently of stateful, rw holes for data and configuration on “immutable” distros.
Second, immutable distros are primarily a distribution and update mechanism that vastly improves the current model of running X number of package updates and scriplets on every machine and hoping it works. There’s nothing that stops you from remounting a filesystem as rw at least on any of the distributions that I know of. There’s also plently of stateful, rw holes for data and configuration on “immutable” distros.