To your point about different time and place, yes, but that’s the system: the jury you get, absent a mistrial, is the jury you get and their opinion is what decides what you deserve by definition (absent new evidence, appeals, etc, within the confines of sentencing regulation, etc.).
Perhaps what you’re after is that there’s no universally objective standard of what a person deserves for their actions, given all the myriad influences and conditions that lead to a particular moment in a person’s life, and which may lessen that persons agency. Therefore the judgement of society is imperfect in the sense that it cannot adequately grasp all these attributes, and may give attributes differing weight based on something as small as whether their eggs were over cooked that morning. So for a person to use the word “deserves” with authority is flawed because a person or people cannot render a perfectly objective judgement.
I think you’ll find that this is an argument as old as time, but whether by birth or immigration, people living in a system operate by its rules, and the word “deserve” reflects the authority of a society to bring down punishment on scofflaws. Like when I tell you something is “cold” we need not debate the true principle of what cold means, you assume to context. So should you assume context for the word “deserves”. Society has never achieved perfection in balancing agency and justice but herein lies a predictable truism - if you run around with a band stabbing others so severely that some die and by luck some don’t, society will determine ya dun f’d up.
It was adopted directly from the British system; Americans had some recent experience with and anger about being subjected to fairly novel (at least in their breadth of application in the colonies) exceptions to the norm of trial by jury and the guarantee reflected a reaction against that experience, but trial by jury wasn’t an American innovation.
Having a set, non-nebulous constitution at all, was unique but the claim that trial by jury “ a pretty unique thing about the American system of checks and balances” is false, it was a well-established basic right in the common law system and the deprivation of it in the colonial administration was a fundamental grievance of the American independence movement not because they had some novel ideas about basic right but because they sought it as a deprivation of the rights they saw themselves entitled to in the British common law tradition.
How was France doing with TbJ? How about Japan? China? Russia? Shall we go through the list of countries in the late 18th century to do this by hand? Tally them up and see how many had a guaranteed right to TbJ for criminal offenses by their citizens?
No, the statement I made holds, and you’ll find that by looking at how other countries adjudicated criminal offenses at the time (not just England). Guaranteed TbJ was the exception, not the rule.
My main point is that in a democracy one shouldn't take the law that exists in a particular place and time as some absolute that cannot be questioned because those laws can and do change through political action, as has recently been happening with drug laws and mandatory sentences for drug crimes.