It seemed to me the bulk of the frenetic scrambling and hounding was done by the front five of Suarez, Allen, Henderson, Sterling and Coutinho. The rest formed the mop up crew that stepped in to close out opponents in our half when the ball had slipped through the first line of traps. Lucas was not as involved in the hounding, which is how I remembered it. However, he did his fair share of work in positioning himself to cut out passing lanes when others were trapping, and closing down now and then.
Lucas' role in this setup is something a less athletic or pacy Xabi could still play; a less energetic Gerrard could do this just as well IF he could ever be disciplined enough and his mind focused enough on performing this "boring" role.
I think it's also about options - we may not press and hound as hard in every game - there will inevitably be some games where our energy levels drop, or games where opponents do the same to us and we need cooler, wiser heads and people capable of making accurate, quick passes to break traps or searching long passes to bypass them.