While the system provided apps were, you could strip one platform or the other out of apps to use less disk space

Yeah fat binaries use twice as much disk space

They did not use twice as much and if it really bothers you there are/were tools that can “clean” the other architecture binaries off the disk.

The resources (images, videos etc) take up the most space, and should be shared. It’s just the code that’s taking up extra space, and there’ll be a way to thin the binary if you want (there was last time anyway).