Great post. I’ve been thinking and reading a bit about saving vs donating over the last couple of months and more or less came to the same conclusion. If you don’t have any substantial savings; it is most likely best to save first and donate later, for the reasons you listed.
Personally I live relatively frugally which enables me to both save 10 % and donate 10 % of my income, and while I believe the overwhelming majority of people in “rich” countries are also able to do this, people are just too used to unnecessarily expensive standards that it is not a viable pitch to have. Having donate 1 % and save 10 % as an introductory pitch makes sense to me.
I also recommend MrMoneyMoustache’s blog, which GeorgeBridgwater already linked to in a previous comment.