I was somewhat expecting this argument when I wrote the comment.

The thing is that argument only works at the policy and governance level of EA. If I'm an individual who is convinced on the philosophy behind EA, and I'm willing to place it before anything else, then it doesn't matter what's optimal to “ensure commitment” because I'm already committed.

That's why I mean when I say that sustainability isn't a good general argument: it can help you in some cases, but not all. Examining EA as a system of values, that either suggests that EA is insufficient or that self-care shouldn't be that important.