Conversely, just because the rider doesn't have the skill to ride the bike in certain conditions doesn't automatically make it the wrong tool for the job. If a complete newby gets on a 990 and falls in the sand on his first trip through Namibia, does that make it the wrong tool for touring Namibia? No. I'll hazard a guess and say that anyone who has trouble on the 690 doesn't have the skill to do the same terrain at pace with a small plastic anyway
I have to disagree with your statement.
I managed to ride my Tenere up Penge without much fuss and can promise you that it was the wrong tool for the job. My friend could not get his D/S bike up the same pass but on his 610 and 525, he barely broke a sweat

Big bikes and short legs results in lots of despair when you run out of traction and the simple truth is that more often than not, riders unintentionally find themselves breaking their expensive bikes while riding the wrong terrain, which leads to downsizing to smaller bikes for technical rides or bigger bikes for long distance adventures.
Where is the 690's niche?
Is it better at enduro/rocky climbs than a 450?
Is it better at doing 300km/s of dirt highways than a 990?
Is it better at 2 spoor than a KTM530?
The way I see it, in a race like Baja 1000, where you can pitch up with any displacement, the 450's are being used, simply because they are faster at doing 2 spoor, open dirt sections and rocky climbs.
So the 690 is not the "best" at anything but good at doing everything and sadly, it seems that most people are not content with "good" anymore.