I like to use a separate "focus" command because I want that command to mean, very specifically, put all your attention on me, we're about to do something. I don't use my dog's name for this because his name gets used in so many other contexts, whether I'm praising him, talking to him, talking about him. And just because he hears his name doesn't mean I want the super intense attention that I ask for in a "focus" cue. So while his name can certainly get his attention, it's just because he's familiar with the fact that it refers to him. But if he hears "focus" all his attention is immediately riveted on me no matter what he's doing and he's ready to work.
Honestly, it would be way more confusing if I expected him to be able to magically differentiate between hearing his name because I want his attention right now versus hearing his name because I just happen to be talking to him about my day.