It's been damage per second in every game forever

So what? It literally means the same thing and works interchangeably

It doesn't tho. Not trying to be rude or argue but there is a big difference. Damage per shot would be like "hey my rockets do the most damage per shot." True but they fire slow and reload slow. Damage per second is damage divided by time, allowing you to calculate exactly how much damage a weapon does each second. Such as, "my black spindle does a ton of damage per second because I don't have to reload."