[snip]
>
> You are confusing a simple config file that is read once and for all
> during boot time (the config file on raspberry pis) with the complete
> installation of a new system. They are not even comparable. There is
> no thing like "oh I re-run the installer configuration to change the
> layout of my partitions".....
>

No, building a system under the concept I am trying to describe is a two step procedure.
You are still merging both steps into one.

Even simpler explanation (so simple it is wrong).

Stage 1) install kernel using program 1 from installation media.

-- reboot --

Stage 2) Install GNOME using program 2 from running built system.