You should buy nicer coffee beans - if your coffee tastes bad without milk or sugar and tastes terrible when cold, that is a sign you are buying trash coffee beans.
This seems like a pretty weak observational study. This is "maybe" a link. The huge elephant in the room is the same one that finally debunked the daily glass of wine is good for the heart myth. People who drink 3-5 cups or more or less are heavily influenced by other life factors that could be the causation for the "maybe link." Initial health, income, work/physical activity, stress, ethnicity, diet besides coffee, sleep, etc.
If coffee really has a significant benefit for heart health, you'd think there would be a scientific experiment created to test this theory. It wouldn't be blind, but it wouldn't have to be for an initial experiment. It should be super easy to find experiment participants, and I'm sure the coffee industry would be super happy to fund all experiment costs.