The point is that this ranking factors in the number of copies of a card played, but that use as a metric can be misleading. Would Vendilion Clique rank higher

The point is that this ranking factors in the number of copies of a card played, but that use as a metric can be misleading. Would Vendilion Clique rank higher on the list if it weren't legendary? Probably. It's not that it's a less powerful card than others higher up the list, it's that you get diminishing returns for playing more than one. The card text on Ad Nauseum prohibits playing more than a few copies in order to make it powerful. If the card worked a different way, such as if you paid 1 life for 1 card, you would certainly be playing four of them. Would it rank higher than the catalysts? No. But that's not the point.