You're making some very bold leaps of logic here, pulling an archaic form of centralization out of your bunghole for the sake of argument, when there are already existing forms of nationalization (Germany, Australia, in limited forms) that have proven perfectly effective. You're also assuming the extreme decentralization the US operates under is inherently more anti-corruption when it is merely more fragmented and corruption can therefore pick off smaller and weaker targets rather than attempt to subvert the entire system at once. And indeed this happens to frequently, with swing state districts and counties showing massive and virtually impossible data outliers that have chosen presidential elections.
If you want to compare the U.S. election to one of a similar scale, you have to look at the European Parliament elections, which are organized by each individual country according to their own rules. You are essentially comparing two very different systems. Not only does Germany have about a quarter of the U.S. population, but it is also more than 20 times smaller geographically. Furthermore, its democracy is more parliamentary than presidential.
Governments in Germany are usually formed by at least two parties, and the president has no executive power.
You still haven’t addressed how a nationalized system would safeguard elections in swing states. The greatest threat to free elections comes from the federal government—it has the most at stake and the most leverage. Giving it even more power doesn’t seem wise to me.