There's also better metrics than "how much money does the charity take off the top" which you can learn about in Will McAskill's book "Doing Good Better," namely you can try to track things like "how much good are we doing for the amount of money we get." The main idea is that if a charity can use more of its donation money in order to have a better impact, then that's what it should do.
Often money earned, lent or given to the least well to do has the highest velocity in changing hands, resulting in much more positive economic impact than if the money were given to people who were better off.
Then the 40% of inefficiency may turn our to be not as bad.
Caritas has very little overhead because they work with voluntaries (mostly).
But yes, there is always overhead.