But...but...the DR, man...you're completely ignoring the DReaded DR issue!!!
I struggle with DR all the time at high ISO. I've never had a situation where Canon's base ISO DR was insufficient AND a couple more stops would have made it sufficient. I've had one situation where 20 more stops would have made it sufficient, but I don't think even the lenses can support that much DR.
agreed in principal
I can't say that I have never seen a case where a stop or two more DR would have solved all problems, but it certainly would not have hurt. Very often it would be quite nice to have.
I also can't say that I have hit conditions where 20 stops would have been sufficient....
But I can say that I regularly hit cases where 5 stops more DR would be needed....
The worst case I have hit so far (this year) was when exposing for the dark areas it was F2.8, 1/25 sec, ISO6400 and for the bright areas F6.3, 1/640 sec, ISO160. That's 12 1/3 stops, a far cry from 20 stops, but no way would an extra stop or two of DR made any significant difference.