Every player has such games, not even Ronaldo is an exception to that and even Messi is rather anonymous if his team is dominated. Dybala is easily a top 5 play maker in the world and has excellent output, last season as well. Ronaldo broke records, yes, but in large parts this had to do with penalty calls in Italy being all over the place. It's not normal for a player to score 12 penalties in Serie A. The same goals for Immobile.
I mean, if Dybala isn't world class I wonder who is. There are not many players in the world who are clearly better than Dybala right now. Especially since Dybala is proving it since years:
2015/16: 19 goals, 7 assists in 2463 minutes (94 minutes per scorer)
2016/17: 11 goals, 7 assists in 2153 minutes (119 minutes per scorer)
2017/18: 22 goals, 5 assists in 2354 minutes (87 minutes per scorer)
2018/19: 5 goals, 2 assists in 2137 minutes (305 minutes per scorer, this was the season Ronaldo joined)
2019/20: 11 goals, 11 assists in 2165 minutes (98 minutes per scorer)
All that on top of being one of the best play makers in the world. I find it hard to argue he isn't world class.