It does cost a fortune to run. Considering every case meticulously on a case by case basis is exactly what they should be doing. That is not an idealistic expectation, it is a realistic one.
To have an effect, condemnation has to be of sufficient magnitude, such that the problem is acknowledged and recognized. It has to be necessarily grandiose in its nature. Given that you agree that the system is not fine, and can improve, where does your contention lie? How can you deny a problem from being recognized if you wish to solve it?
"Mr Prosecutor, yes I killed that guy. But in my defense, my wife was shouting at me earlier in the day and it made me upset. I had been fired from my job the day before, and didn't have a new job lined up yet. So I got angry at the grocery store over raising the price of milk, and killed the cashier. Please consider this and drop some of the charges."
"Ohhh your wife was shouting at you? I hear ya, buddy. I'll drop most of the charges and you won't have to go to jail for murder..."
I mean, come on. We can't take people's personal circumstances that are unrelated to the crime into account. No matter if you are rich or poor, married or single, working or unemployed, kids or no kids, you should get equal treatment under the law. I can't believe people are arguing that "possibly suicidal" people should have charges reduced. If that was true, everyone charged with a crime would claim to be suicidal...
The logical conclusion of what you're suggesting is a system where only outcomes are looked at and assessed, little about the person leading up to outcome is understood, and nothing is learned, because it's somehow unacceptable to understand individual circumstances. But surely you see that it's in our own collective interests to learn why things are the way they are, instead of just indiscriminately slapping parking tickets on everything that looks bad and hoping our problems will go away?