I think you just made my point while arguing against it.
I agree with user specific data being stored in ~/Library/App Support; my problem is with system data being stored there.
From what I gather, Apple has now moved ALL update data into ~/Library/Application Support/App Store/updatejournal.plist of the user who installed the updates, so records of the installation of Deltas/Combos, updates to Apple apps, security updates, etc. may be scattered between several user accounts on a Mac with more than one user...with no apparent way to see a complete history in one location.
That, I still think is counterintuitive.
I hadn't thought of this before you brought it up but it appears the segregation is being handled by the ~/Library/Application Support/App Store/updatejournal.plist. A reasonable work around.
Reasonable only until it intrudes on the OS's territory.
BAS (Before App Store) many apps were installed in the user's ~/Applications file, but some years ago Apple deprecated the use of the ~/Applications folder in favor of putting all apps in /Applications. More recent installations no longer include a ~/Applications folder.
I got into OS X in Jaguar, and I can't say whether ~/Applications was present by default back then, but I can definitely say that
waaay back at MFIF, i.e.
many OS versions ago, V1 advised us that even though the folder wasn't present by default, it would show Apple's standard /Apps folder icon if you
created it, and that still holds true in Sierra.