A Mediocre Lawyer not winning a winnable case = not a good thing.
Say a starving child steals a loaf of bread. The law says all theft is at least 1 year in prison. But the judge can see that the child is actually destitute and it was his first time. The judge could shorten the sentence to 1 week; that's fine, there should be room for interpretation and leniency.
But it should NOT depend on whether that child had a persuasive lawyer or not.
A good "AI Lawyer" would simply behave as how ALL lawyers SHOULD: Simply present the facts, the laws that apply to those, offer suggestions for the verdict, and the possible long-term consequences for each possible verdict, without injecting dramatization, exaggeration, or attempts to pull at heartstrings etc.