Worlds is definitely a much harder tournament than nats. At nats you are pretty much guaranteed to play a few rounds against amateur or worse players, which puts you at 3/4-0, meaning that you can go about 3-3 against top players and still make cut. At worlds you play against top players all 7 rounds no matter what. You have to go at least 5-2 against top players instead of 3-3, which is much harder. 5-2 doesn't even guarantee top at worlds anymore. I went 5-2 losing my last round this year and I didn't make it. Worlds is uncomparable to nationals as far as difficulty goes.