I know that and would handle my personal system upgrade differently (no update with the GUI, only via terminal to see the messages). I was playing from the perspective of a new manjaro user with a completely fresh install from ISO and the very first system update, before even trying to understand the system, reading forum posts and wikis.
Since this is that important, I would suggest that a message window opens with pamac during the very first start that explains this and even better links to the wiki.
Otherwise, potential new users could directly turn away from Manjaro after such an experience before even having a chance to get to know the system better and understand.
anyways, this sounds similar to what happened here: Unable to boot manjaro after failed pamac update