I don't see it quite that way.
Canon improved a LOT from 5D2 to 5D3 on the areas people most complained about: AF, weather sealing, ergonomics (aka dedicated buttons).
And still managed to focus on new lenses and flash that just leave the competition drolling: 70-200II, 24-70II and 600RT.
The sensor was left behind. OK. But if you consider the 5D3 as a wedding/news camera, then the DR and resolution advantage of the D800/D800E goes down the water. No in-field news shooter will want a gazillion megabytes file just so can crop the hell out of it, and DR is important but they can live without it. Same for wedding shooters.
Now, if you consider Landscape and Studio shooters, then OK, the D800/D800E is the route to go definitely.
A few years back Canon had the junk because of its pitty AF.
Now Canon has the junk because of resolution and DR.
If they fix it on the 5D4, I am sure someone will show up and say "Oh, but this camera stinks! The D900 has a popup flash!"
News people probably wouldn't be shooting RAW, so file size is considerably smaller. Wedding shooters don't want DR and an extremely detailed image? First I'm hearing of this
As for holding Canon accountable, none of the issues that have been mentioned are a 'popup flash' as you put it. They are real issues that affect users.