Mrs Quinn, I don't believe anyone is questioning the class of Sergio Parisse and neither is anyone suggesting that only one player per position be descibed as world class.
The All Blacks are currently considered as the best team in the world and set the benchmark for aspiring world class players from other international sides, and comparisons between players will always be made. I mentioned Read and Vunipola, two different players with different qualities who can both be rightly described as world class, and I would suggest those of Vunipola would not necessarily be conducive to what the All Blacks are currently looking for in a no.8.