Imagine casting a "speed ×100" spell on a dumb person. Would that make them a smart person? No.
There's a line in the book WYRM that made this fact click for me many years ago. The paraphrase is "A dog that can think a hundred times as fast will take a hundreth of the time to decide that it wants to sniff your crotch."
From Scott Adams Blog
The article really is about speeding up government, but the key point is speed as a component of smart:
This shifts the focus from the ability to grasp and think through very complex topics (includes good working memory and memory recall in general) to the ability new topics quickly (includes quick learning and unlearning, creativity).
This also changes the type of grit needed. The grit to push through a long topic versus the grit try lots of new things and to learn from failures.