The benchmark announced in the article seems to be around weird edge cases (which are often important) and whether it can prompt the person with relevant information rather than just listening to what they want to do.

Top tier tax professionals can do pretty well on this benchmark (better than agents) but won't hit 100%.

The kind of people spending time preparing oodles of returns would not do very well on this metric, though (especially midway through that pile of returns, as opposed to "think carefully about this trick question").