Even for those looking to use their donations to set an example, a donor-advised fund would have many of the benefits and none of the downsides.

Still not so sure. Legibility and inferential distance are major constraints here. When trying to explain earning to give it's much easier if the "give" part is something obviously good. Donor-advised funds combined with an intention to choose effective charities aren't "obviously good" in the same way as a donation to a charity.