Data transfer isn’t a finite resource like oil or gas.
This also ignores that not everyone has stellar connection speeds, and that some people -do- have bandwidth caps (also, let's ignore that people are often mobile). Developers really need to stop making assumptions about people's hardware or internet speeds... and just do their jobs and make efficient designs. Maybe one day everyone will have super beefy machines on fiber optic networks with 10gb nics, but that's not the reality as of now.
If a patch needs to be 2gb, then so be it. But if it could be 100mb, then that's certainly better and something to strive for.
It absolutely is for many people. Not everyone has unlimited services. Even on fixed line services many are limited.
Clearly you haven't seen those crappy limited data ISP contracts floating around. It's an issue for some people.
Apple is known for providing ZERO official guidance on the lifecycle of security updates for older versions. It really looks like they're trending towards an iOS model where there's no concept of support for anything but the latest version. (The one exception is that older iOS devices stuck on iOS 12 have still been receiving updates)