Groundwork widely regarded in Judo as both easier to learn and requiring different if not less fitness. The main difference is that standing work requires explosive power, whereas groundwork is more static strength. Technique will bridge the gap, but when standing work takes longer to learn, your experience is that throws take more power.
Also, groundwork tends to be slower and like a flowchart, whereas standing work requires instant decision making and many more variables.
Lastly, high explosive power fades from the 20's on, so it's natural to continue on to ground work in your later years.
Given these clues, I think what Helio really did was be one of the early groundwork specialists in Brazil. He termed it as using leverage because he probably didn't recognize when leverage was used in throws, and not all throws are based on leverage. Unlike ground techniques. Thus I don't think Helio actually changed the Judo ground style, except that he focused on submissions for vale tudo.