I’m thinking it should be less (I just have the browsers there if needed and do not use). I’ve checked the cache folders for each browser and this only seems to add up to 100-200mb.
I didn’t realize the GUI would account for 2GB of space.
DietPi themselves are just bash scripts located within /boot/dietpi. The rest is Debian or Armbian OS. Size depends on your software title installed. Using a desktop is already some larger thing, that of course needs some disk space.