Whether it’s accurate depends on what you’re trying to measure by it, I guess. “Hot” can mean many things.
Is the goal to find out which artists stand to rake in cash in the immediate future? Which ones stand to get the greatest leap in name recognition? Or just which ones are going to be heard most times by human ears? It could all be very different. Back when it was just a simple measure (say, radio airplay) Billboard didn’t have to worry too much about what they were actually trying to measure. Now they should probably get a lot more explicit about it.