I agree that waiting is a good idea. You really don’t want to tempt fate by relying completely on an abortive update sorting itself out completely in the event of an interruption. On Windows they say Do Not Turn Off Your Computer, for this reason.
But I would say there’s a general problem with Apple’s update UI. If things look stuck, customers will naturally assume that it has stuck. Personally, I’d like to see more detail than a line crawling (or not crawling) across the page. Worse of the worse is where you get the line starting again from the beginning for no good reason. That doesn’t even look slick. It looks like something is messed up. More information = good.
One issue -- Apple's updates now not only modify the system files, but can also touch the Boot ROM and firmware.
Second issue --an opaque UI to insulate the average user from the updates process works best when the process is reliable, which it sometimes isn't.
The old days of downloading a .dmg, opening a ..pkg, and watching the Installer.app do its thing was fine, but not a "modern" UX where the assumption is that users shouldn't have to worry about such things at all. Even when that old progress bar seemed to slow down or stall, at least there might be sounds (or lights) from the hard drive indicating that some activity was occurring in the background. The Downloads section of the Support site is now a shadow of its former self, and I wouldn't be surprised to see it deprecated entirely in the future.
At least the progress bar is better than a spinning gear (or the juggling balls in Windows) in the sense that it gives some idea how far along the process is, even if it's probably not very precise, and the time estimates are usually wildly off.
The real puzzling thing is that Apple is not entirely averse to keeping users informed during an update, but ironically, it's with the most appliance-like Apple product of all, the AppleTV, which does provide indications as to what it's doing, and what users should expect, to complement the progress bar.
My Mac rebooted twice during this last Mojave update, and I have no idea what occurred at any point along the way.