Really? So why bother creating nightly GApps packages? Seems a pointless waste of storage? If the logic is to only flash OpenGApps with a new ROM then surely a monthly package would suffice? AND this would be clearly stated on the OpenGApps website as well as in the 1st post on this thread?
I think you are trying to push your own process on other people and pass it off as 'the standard'. It isn't. Not everyone's device has oodles of storage available in the /data partition.
Flashing OpenGApps stops your RW /data partition being filled up when there is space in the RO /system partition. Why would you want an old version of an app wasting space in the /system partition when you install a newer version of the app that has to go into the /data partition?
By all means tell yourself your process is correct. Just don't push it on other people.
End of discussion for me.