Delta will have a better idea than anyone what the demand is. They operated two flights a day (Boston and New York) in 2022, so they'll know the market well, and clearly feel there's a demand for another flight. Flights to new destinations open up new markets - there might well be a lot of people in Atlanta who decided they didnt want to travel to Scotland as it meant connecting. Now they can do it non-stop. Also opens up much more convenient connection opportunities to Florida and Central America/Mexico.
Let's not forget that the US flights were averaging around 95% load factors all summer, and there was no sign of any price dumping, so there certainly seems to be plenty of demand. I think they will do just fine.