It's crazy that even dot releases are a full 3.6G download
Binary patching hasn't been a thing for years unfortunately. Even bigger wreck on consoles these days, where an update can be 50+ gigabytes...
True, and it's fair to say binary diffs aren't worth the complexities they introduce anymore, yet the concept of only pulling updates for individual packages has been a thing for over two decades in the *nix world. It seems like a poor choice for Apple to not bother making updates more discerning while also removing binary diffs... certainly a shitty move for anyone without a 99th percentile internet connection - then again everyone outside of that group probably can't afford Apple products anyway.
For some perspective: 3.6 GiB is significantly larger than the downloads required to install my entire OS from scratch, and 36 times larger than my average weekly run of apt.
From my now outdated experience on Mac OS i'm aware they do divide things into installer packages with some kind of receipt for version info that software update probably probes. So I guess it must be that these packages are not very granular.