Ginormous update sizes are definitely a regression. There has been some reporting on this recently and I can't remember the details, but I believe it is due to

Ginormous update sizes are definitely a regression. There has been some reporting on this recently and I can't remember the details, but I believe it is due to a wanting a combination of: cryptographically verifiable updates; atomic updates (avoid the risk of a partial update); and shipping the dyld shared cache directly. These aren't insurmountable limitations, but it seems like Apple chose the path of implementing these in a simple way (at the expense of bandwidth and storage). One would assume they would want to then go ahead and figure out how to implement this with a slimmer delta update, but who knows.