If the split-electoral-college vote system used by Maine and Nebraska had been in use for all States in the last few elections, and the popular vote had been exactly the same, it would only have changed the result one time - Romney would have won in 2012. And Bush and Trump would both have still been elected President having had fewer popular votes.

So it wouldn't necessarily have solved much. (Of course the change might have altered the voting pattern, since "swing states" wouldn't be the only significant ones any longer.).