"I think this is a very complicated issue... and I suspect I'm not unique in this sense (either). On the one hand, if we by progress mean more difficult climbing, a significantly harder problem or route must get a higher grade, because it's on open ended scale. On the other hand, it's not always easy to know whether the thing you've climbed (this is even more true for bouldering) is just very hard (or easy) for you, for any number of reasons (body type, specific strengths or lack there of, skin type, flexibility or lack there of, style, rock type... etc., etc.). 8A for one person can be 8C or even impossible for another.
Also, as a grade is not a dot, but a span, how much more difficult must a problem be to warrant a higher grade? And again, how much more difficult according to who?
It's great that Daniel speaks up and tells us what he thinks. More world class climbers should do just that.
In the end, consensus is impossible.
Video of Daniel Woods attempting The Game, a potential V16.