I’ve always been puzzled by the discrepancies in app update sizes, app sizes, and actual download sizes but never bothered to measure it. My bad. I will experiment right now as I’ve a widget that can track data use. Here we go.
The AppStore says Facebook is 230MB. I am downloading it and tracking the download size - it’s 137.59MB. I can’t confirm if this variation holds true for the update as I will have to wait until the next update is announced. But it seems likely that the update too will probably being not as big as listed.
You are right. Assumption is the mother of all… Least I can do is add an edit saying this. Thank you for pointing me in the right direction.