Yeah, there have been countless combo decks built around pretty much the exact same set of support cards. Individually the support cards usually don't appear to be a key part of any given deck, but to a large degree that's because no one would ever call a deck a "brainstorm deck" even if brainstorm was the central card the deck was built around. They'd name it after the other things that go well with brainstorm, because that's the part that's actually different.

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.