I was on a jury in Texas that sentenced a 21 year old mother to 11 years to prevent a judge from probating the sentence just because it was a first offense. If a man had committed the same aggravating actions, we probably would have sentenced him to 20 or more years.
The Jury only knows the facts that are permitted into evidence.
In many cases, past offenses are not permitted to be referenced. Evidence that had an error in the chain of custody is suppressed. The prosecutor and defender take turns kicking people off the jury, so the people who look the kindest or smartest are gone.
Jury trial is indeed better than the French system where judges both run the court, and decide, with noone on the side of the defendant.