It is close - Hewit´s W and US open is maybe better than 2x AO, but GS is not everything- Hewitt has edge in that he was No.1 in world, Djokovic wasn´t, but don´t forget Hewitt biggest achiements came in era without Roger- Rafa and he was No.1 in transitional era just like Roddick - Roger just wasn´t that great player, and Rafa wasn´t at ATP tour, and Hewitt was great in beginnings of his career than he wasn´t so great. So Djokovic 2 AO titles are in harder more competitive times with FEDAL here, Djokovic also had more Master 1000 titles -Hewitt was in 7 finals and won 2xIW- only 1 Master tournament in whole career. and Djokovic already at his age 23 was in 11 finals and won 5 of them.. So it is close but every tournament and with every bigger succes will Novak getting the edge over Hewitt.
You nailed it. The fact that Novak got his two slams in the Fedal era proves he's much more accomplished as a player than Hewitt or Roddick.
Plus he still has his better years ahead of him.