I'd guess that about 1/10th of the church donation ends up being spent on what most people would call charity and the other 9/10ths gets spent on ministry.
So I'm therefore giving about 1% of my income to "charity" but probably getting credit for 5.5% because Brooks (and others) lump that ministry giving into the figure.
Obviously I believe that that ministry giving is super important because I'm very religious, but I think that using ministry giving to claim that religious people are more compassionate is silly.
Christianity isn't a contest about who's nicer, and as a Christian I do not want to be compared to some "other" who isn't as "compassionate" according to Brooks or anybody.
This book is very likely just conservative propaganda that drives motivated reasoning.