Not sure, what you mean by this. We are not the Calamares Devs. So what devs are you referring to here?
What do you mean by system programs?
A linux distribution is a distribution of a large set of 3rd party applications, really. Anything besides the kernel it self can be considered 3rd party.
I would define “system programs” as only what the system needs to actually boot and function. So that disregards any GUI stuff at all, since that’s not needed for a system to be functional. A GUI might add functionality, but it is far from required for a system to work.