The copy on the console was on a disc that is Blu-ray density: dual-layer.
Dual-layer Blu-ray is 50GB of storage space.
The PC version has more settings, updated graphics, more content, etc. The console version likely did not have even a full 50GB of content. But, the PC Version, with the patches, updates, and upgraded graphics/sound, should take up much more space.
The 7-disc set is a set of DVDs. DVDs do not have nearly as much storage space as Blu-ray discs.