Perhaps Buffett doesn't have a singular genius for applying his wealth to charity. It's anti-democratic on its face to just surrender control of "what problems are solved" to a single person, regardless of the decision metric. Is it truly better for one person to control all of that on a whim? Even assuming the best of intentions, he may pick a disease charity based on a close association with a victim rather than any broad rational analysis. You're just hopping right on board with his unquestioned assertion "I'm better at picking," did you give that one any pause or just hopped right up to carry that water?
What are the problems that governments are 'often' poorly suited to solve? Would governments be more or less suited to deal with these issues if they hadn't been defunded to support the personal wealth and charitable whims of billionaires?