Imo one of the reasons these exist to begin with is that the judges did a crappy job meting out "justice" as perceived by the voting public. So minimum mandatories were passed to ensure that SOME justice was handed down even if the judge would have given them a slap on the wrist. Not that I agree with it the way it is implemented now, but I have a close to home example.
Just over 3 years ago my bro-in-law was killed on his motorcycle by a 20-year-old kid who had THC and booze in his bloodstream and was texting while driving over the speed limit. He hit my brother-in-law, who was sitting on his bike at a stop light, at right around 75 mph, fast enough that he killed my BIL instantly, and so hard that his helmet was crushed and the force of his helmet hitting the minivan dented and BENT the A-pillar (windshield pillar) of the van. It also almost killed his GF who was in the passenger seat. In fitting irony, the driver walked away, because the one thing he did right was have his seat belt fastened. They tried him with everything they could, vehicular murder, which I had never heard of before that incident. It carried a mandatory minimum, iirr, of 5 years, with possibility of life. The judge gave him the MM because "he was young and has his whole life ahead of him". So the scumbag that took my BIL from this earth, a family man with a kid, wife of over 20 years, and was a decorated war veteran from BOTH gulf wars, was out of jail this summer, time off for good behavior or some other ****. The judge wanted to give him probation, but was forced to give him the mandatory minimum. Was justice served? Imo, **** no.
As has been brought up before, different versions of the same crime. It is a tough nut to crack that is for sure.