Well, I supposey ou could completely remove them and save about 100Mb on each, even though removing them would be a very difficult and time consuming task as there are a lot of libraries involved and finding out which are needed and which are not won’t be easy…
By far the easiest way (imho) would be to just not install KDE or Gnome when you’re installing the system…
I suppose others may have attempted something similar to you and may be able to give you a detailed list of things you can safely remove 