I agree with you. I think the author missed some pretty significant stuff, including the metaphor of Buffy diving into adulthood, the "same blood" stuff (which gets repeated in Potential), and other factors.

That said, I think his argument fails on its own terms. While Giles wanted to limit Buffy's choices to just two, in fact there was a third option. That doesn't negate the difficulty of choice, it means that we have to explore all the options before deciding which one to choose. It's like the situation in GD: we think the only 2 choices are letting Angel die or feeding Faith to him, until Buffy reminds that her blood offers another way out.