True. Still, I'm not sure of where an isolationist US playthrough would go. If it's just never going to war, no player will ever take it. Maybe you could focus on Japan, but the Tri-Partite Pact is probably going to draw Germany in. If you just wait until the Axis powers attack you, well, that doesn't change much compared to a historical playthrough. Not only do you have to disable the focuses like "The Prussian Menace", but you also have to neuter those who make Japan or Germany strike first. In a sense the historical path is "mildly isolationist" already.
Well, you *could* make the US create their own faction and tweak the focuses so they never fight Germany, but if it's just US vs Japan, that won't be a very interesting fight for the US player.