Well the grade 3 power was also showed to be something incredible that surpassed Cell's power. Its only deficience was the speed, that wasn't on par with the chi level output, so if someone showcased that level of power but with speed that matches said power, those reactions would make as sense as if it were >>> grade 3 imo.
As for what you said about "how strong they expected Cell to be when Goku said 'there's no telling...' "... they also expected Cell to be way stronger than their initial estimations when Kamiccolo was told to be useless, right? Yet they were all blown out by 100% Goku, meaning it surpassed all their expectations. What does this mean?