> One could argue that Carnegie's wealth was itself a failure of good governance
I'm not sure there's a specifically compelling argument here. The man brought the Bessemer process to the US and basically invented the idea of vertical integration. That all made steel cheap enough for the US to rapidly industrialize. It seems like a set of accomplishments worth financial reward.
> and that these rules he made about giving away that wealth are paternalistic.
The culture of the wealthy at the turn of the last century was such that they believed their good fortune obligated them to help society and the poor. This was part and parcel with the late 19th century and early 20th century progressive movement.
Moreover Carnegie actively worked against some pretty nasty things the federal government was doing. At the time when Woodrow Wilson was re-segregating the federal government and showing Birth of a Nation in the White House, Carnegie was funding the Tuskegee Institute. At the end of the Spanish-American war, Carnegie butted heads with president McKinley and tried to secure the independence of the Philippines and joined the American Anti-Imperialist League.
Regarding your claim of a "policy failure", to what end would the government of 1900 have used Carnegie's money had they seized it? It likely would have fueled the occupation of the Philippines, Wilson's racist and messianic madness, or some other horrific endeavor. Yet, Carnegie used it to fight imperialism, build libraries, and aid the poor.