Why does this sourdough recipe call for 2 and 1/3 cups starter? Isn't that too much?
That is quite a bit of sourdough starter, but not extremely so. In sourdough recipes that also include yeast in the loaf, you might see measurements of a cup or less, but a tablespoon of starter in a loaf would be pretty negligible.

The recipe here does not include yeast other than what's in the starter, so 2 and 1/3 cup is not extreme. I watched the video; there is no reason to think that the recipe is in error.