I believe King being referred to as the top of the All-Stars is the whole King>Queen>Jack theme at work. I mean, King does not have a separate designation as a leader but he outranks Queen, who, in turn, outranks Jack. So King is called the top/the first of the All-Stars because he ranks the highest among them. I think that's why some translators aren't agreeing with others calling him their leader because it doesn't mention the term leader. Also, It's because this^ talks about their ranks that the VC writers felt the need to confirm King is also the strongest crew member after Kaido.