Now, the legacy approach isn't perfect either, as you may have caught on. Instead, all subsequent game updates used a single new bar archive file which would contain all post-release game changes (but nothing else) and any data placed in this archive would "override" everything else anywhere in the other bar archives, therefore all the baseline game data could just stay there and rot forever. Looking at how things worked on legacy AoE3, there the devs basically had all the huge bar archives set in stone when the game/xpac initially released and that was it, they would not change them afterwards. I would say there are currently more pressing issues in the game than this, but it's certainly something that would be worthwhile to look into improving.
#STEAM DOWNLOAD DROPS TO 0 DISK USAGE UPDATE#
The disadvantages of this update approach are obviously very high disk usage while gigabytes of data are being worked with, and also high disk space requirements in order to essentially store a significant portion of the game twice at once during this process. It only downloads changed files (which are relatively small), then it uses the existing installation's data + changed files to create those big updated bar archives in a temporary folder, then once that's all done the new bars are moved to replace old ones and you finally get to play again. It doesn't have to download the entire game from internet though, that is not correct. Yeah there is nothing you can do, that's how the DE update process is implemented repack everything into the huge bar archives.