The thing about jury nullification is that it isn't a checkbox.

For example you could argue that the OJ Simpson murder trial was a case of jury nullification. It probably wasn't, the jury just came to a conclusion many people disagree with. In fact OJ was found guilty in the civil trial. Was it truly just the difference between "beyond a reasonable doubt" and "a preponderance of evidence"? Or was it jury nullification? Or were the jury idiots? (In which case?)

Rodney King was beaten by police officers but ultimately acquitted, was that jury nullification?

Kyle Rotten shot people but was ultimately acquitted, was that jury nullification?

Additionally, the same law that allows for jury nullification also allows for the opposite situation. Someone who definitely didn't commit the crime still being convicted.

I'm sure there are plenty of cases where an "unfair" verdict is rendered. Proving actual jury nullification is difficult, unless jurors actively speak out about it, which even then can be risky.