That just moves the problem back one step. The processes that lead to the evidence in the untruth universe can’t be the same as the ones which lead to the similar-looking evidence in the truth universe (unless you get Gettiered, and then the people in the truth universe don’t actually have knowledge.) So if you don’t ignore history, the worlds still differ in ways other than just the fate of Joan.
We are stipulating that we would have the same evidence in both cases, so it would lead to the same beliefs, just with different truth values.
That just moves the problem back one step. The processes that lead to the evidence in the untruth universe can’t be the same as the ones which lead to the similar-looking evidence in the truth universe (unless you get Gettiered, and then the people in the truth universe don’t actually have knowledge.) So if you don’t ignore history, the worlds still differ in ways other than just the fate of Joan.