It has to process all the big .pak packed archives to change a few files inside.
Some of those .pak files are 30+ GB large, so unpacking them, replacing the little files, repacking them, is what takes so much time.
The bad part is that the updater does all of them in one run, saving all the new .pak in a temporary folder next to the game, instead of processing each .pak and replacing the original individually
. Because of that, it doubles the disk space required (more than 160 GB), instead of "only" 110 GB.
Maybe they do that to be able to revert if something is wrong, but alternatively, they could simply verify the hash of the .pak and downloaded update, and the available disk space.
Anything beyond that is easily recoverable.
So that's a way to improve the process, but I know they won't read this Another improvement would be to specify a temporary directory, on another drive.Yet another improvement would be splitting those huge .pak files.
It's rarely a good idea to host such big files on a disk.
But, this is still much better than having to download the whole .pak files again. It would be slower anyway, and take as much disk space.