Building and maintaining such a stripped system requires additional effort. Out of question.But you can rm -rf /usr/share/doc :) You can build custom, stripped down packages (as done for udebs for the Debian installer).
And no, you can buy a bigger SD card.
Accept that you don't have the option of replacing hardware.
> You might wish to forward this report to architects that are
thinking of better design decision for the future.
I'm not going to do that.
Don't. Stay where you are. Debian is not for mobile anyway.