the entire question is not, "is a pop-up flash good enough to produce professional images as good as carefully lit studio images with a full lighting setup?". Nobody claims it is. Pop-up flash is a useful tool when no other lighting options are immediately available. Not more. But not less, either.
the question is: would a majority of potential buyers find a popup flash useful in a specific camera. If potential customers ever were asked - rather than only 10 hand-selected "arch-conservative Canon Explorers of mirrorslapping" - probably around 70-80% of all potential buyers would like to have a built-in pop flash in ANY camera. Especially if that little pop-up also serves as wireless speedlite commander.
The percentage is very likely much larger than those who want "advanced video capabilities" in every DSLR.
And that little pop-up flash also costs very little to implement, otherwise it would not be included in vritually any € 99 powershot digicam.
7D II is "as specialized and professional" a camera as 5D S / R are going to be. 7D II does have a pop-up flash. As had the 7D. Nikon FX cams like the rather professional D810 also have a pop-up flash.
Not many reports about "wheathersealing problems", "broken off pop-.up flashes in the field" around. All those "un-pro" myths are solidly debunked.
No, this is no "rant". It is my opinion.