The question you should ask yourself here is why was justice not dispensed, or whose fault is it that justice was not reached?
The courts were set up based on structures to provide justice, however if there are bad actors (in many cases the police) involved outside the control of the courts than why would you blame the courts for following the same set of procedures that convict guilty people on a regular basis.
Many miscarriages of justice come down to police corruption, planting of evidence, coercing confessions out of people etc. Every system is open to manipulation and these are always related to human flaws as opposed to the system itself.
If your whole point is that the courts can get it wrong than I doubt anyone disagrees with you, if your point is courts are only there to fulfil a role as a legal construct and not to dispense justice then that is pretty dumb.
Why do you think bad actors are confined to the police? Why indeed do laws need to be changed? Is it to administer a different type of justice or is it a recognition that some laws don't always lead to just outcomes.
My point isn't that courts are legal constructs designed not to dispense justice, and to think it was is a dumb interpretation of the statement that "Courts of Law aren't always courts of justice".
Nobody ever said, or even implied, that the courts were designed to deny justice, but the fact remains that there are occasions where they don't give justice while still remaining within the law. And to deny that fact, or to pretend that only criminals would suggest it, is risible.