I think the size may have more to do with the team not splitting up the Unreal build paks. Haven’t checked how well it’s actually split up, but I can say that changing even one small thing could result in a giant update if that build has like one pak file with all the things in it. There are ways to configure it in the build but it’s not a magic toggle either. Worked with a studio handing off UE builds before that didn’t build the game in a split friendly way and it made every upload to S3 take forever cause there were only like two really giant paks.

Also makes me wonder, does Steam not do diff patch style updates for changes within individual files? If not, that could save a ton of bandwidth.