Earlier quoted context omitted.
> it screws up the class curve This is your problem right here. There is no rational argument for grading people on a class curve. That just makes the class a lottery and incentivises sabotaging for others to get an upper hand yourself.
Of course there’s a rational argument to using the distribution of scores to set the grades: If everyone in the class gets half the questions wrong on the final exam, you shouldn’t just fail the whole class! The test was probably just harder than expected But in that same example, if many of the students get close to 100% on the final by cheating, then the remainder of the class will suffer
If an exam turns out to be too hard the teacher can investigate, consult their peers, talk to their students and decide if it's worth to scale all grades by a factor to correct.