Isn't that always the case when you have rule of law and separation of powers? The legislative body comes up with the law; judges just apply it.
E.g. if the law says "murder carries a penalty of minimum 5 years and maximum 30 years imprisonment", then a judge cannot give a sentence of 4 year or of 40 years, even if they personally believe this to be a "better" sentence.
My understanding of the US system design is that the law as defined by the legislative body is in a way "minimalistic" (and even more so at the federal level), and jurisprudence augments it with the details.
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.
IANAL but no, the US claim to minimalism is just branding.
The largest jurisdiction like the Federal judiciary, for example, have the Federal Sentencing Guidelines which have a strict point system for criminal sentencing where judges have little discretion due to a Federal “tough on crime” wave.
It really depends on the subfield of law and the vagueness of past legislation.
> My understanding of the US system design is that the law as defined by the legislative body is in a way "minimalistic" (and even more so at the federal level), and jurisprudence augments it with the details.
Which really makes me wonder, how the hell to even professionals keep track of that? For regular stuff you literally can have thousands of relevant cases going back centuries as "precedent" to build on.
E.g. if the law says "murder carries a penalty of minimum 5 years and maximum 30 years imprisonment", then a judge cannot give a sentence of 4 year or of 40 years, even if they personally believe this to be a "better" sentence.