I don't like the term leadership capital because the analogy misses an important aspect: If the change turns out good, the leadership capital of the technical director increases to more than she had before. So she did not really "spend" it, but rather invest/bet it in/on Figlet.
Also, it is not a single value. For different people the technical director has a different amount of leadership capital. If Figlet turns out good for you, it increases. If you don't like Figlet you consider the technical directors capital as lower. So the amount of capital is actually specific to a relationship between two people.
At the end of the article, the author explains that leaders move slowly, more slowly than they otherwise could, to allow their small changes to pay off before asking for more, thereby earning them more leadership capital. Which I think makes your point.
Perhaps your disagreement is purely around the term capital. You may not realize that, in finance, the term capital implies that it is there to be invested.
Good point about differing levels of trust between individuals, as opposed to groups. It's a nuance the article doesn't really broach.
I was initially taken up with the elegance of the idea, but did a double take after your comment. We haven't really established that trust is transactional...
Also, it is not a single value. For different people the technical director has a different amount of leadership capital. If Figlet turns out good for you, it increases. If you don't like Figlet you consider the technical directors capital as lower. So the amount of capital is actually specific to a relationship between two people.