Maybe Fintan, but he could only play against those playing then and we do judge the “greats” by what they did at the time. Barry John for example playing now would get destroyed but surely he nonetheless deserves to be regarded as one of the greats.About half of the 2015 AB starting team, alone. I don't think he's even in the conversation - McCaw, Carter and Zinzan Brooke are the obvious NZ contenders.
Watching a rampant Lomu was brilliant for the sport, but he was playing against undersized, often semi-professional players. A brilliant athlete and ambassador for the game, but far surpassed since (and before, but less obviously).
That said I’m unconvinced Lomu was the greatest rugby player ever. He was big, very big, and fast too obviously. But once sides worked out how to neutralise him he was much less successful.