Taking your example, what constitutes murder and minimum and maximum penalty are defined in "broad strokes", and the judge gets to define "in this specific case that person is guilty in a way where they should be sentenced to X years", and that becomes law (IIUC scoped to their jurisdiction), progressively refining and tuning the whole system, because the next judge faced with a similar enough case would be bound by it. The lawyer game is then to argue whether the current case is close enough to a previous one for the previous ruling to match (and thus tying the judge's hands). A thoughtful US judge would consider both the case at hand and the implications of being law-generating when issuing a ruling.

"Precedent" is a way of saving the time of courts and lawyers, by not having to argue the same details every time they come up. And it's not as if every court judgement becomes a precedent; only higher courts can set precedents, and they can only be overturned by higher courts still.

I think this is a reasonable way of approaching justice.