I think you’re probably right on this when it comes to donations as it’s less likely that less money would necessarily mean less sleep or time with friends. However, the article seems to be talking more about working, whether that means in a high paid job with long hours, volunteering in all of your spare time or working long hours in an EA role you love. You’re still probably right that many people can push themselves more than they currently are. Any suggestions on how to identify where the line is for an individual would be really interesting to discuss.
I think the right way to do it is to try things out and see what you can do. It’s well known that we can’t easily predict the careers we’ll enjoy or the way our interests will change in the future. The same thing applies when thinking about what would be too demanding.