I agree that 1. is a problem. I think you want to keep things fairly simple for the sake of transparency, which would mean you end up being e.g. unfairly positive towards leaders of asian countries with conscientious populations and strong hygiene norms. One thing you could do would be to add “which is better than other similar countries like X, Y and Z”—but then there is still some subjectivity about which peer countries to include.
I’m less concerned about 2. Even if the majority of voters are impossible to persuade, the marginal voter theorem suggests that you only need to influence a few people. And even in a state where one party has basically no chance, there is often competition at other levels. For example, if Cuomo is the Democrat nominee for New York State Governor, he will almost definitely win—but this might help a rival Democrat challenge him for that nomination.
Your project sounds like a good one… but I agree it would be very hard. Focusing on covid only seemed like a tractable smaller version.