I disagree. First, because there's some evidence that most people will give a fixed amount to charity (I'm too lazy to find a source), so they're playing a zero-sum game and any fundraising overhead just takes away from money being given to people who need it.

Second, because that money doesn't come from a vaccuum. People who spent it on charitable causes could have spent it on other things; some of these things might be a new smartphone or fancy food; but some of them might have been an electric car or a college fund or whatever.

So super-expensive fundraising takes money away from other parts of society, some of which might be productive, to sink it into the giant resource-wasting game that it advertising.

Personally speaking, I donate to the Global Fund. They do relatively little advertising, but they get shit done.

I have heard it is 50%+ that the fundraiser keeps.