Elected judges was an attempt to put the judiciary under some kind of democratic control.
Perhaps that was even a good idea before the days of mass media. Today, judges run their campaigns on how many criminals they put away, not on how well they decide the law.
It's a similar story with elected prosecutors. In Australia, Aaron Swartz would still be alive.
As to grand juries... explain your problem there, I can't even anticipate what your issue is there.
Let me put it this way: Hope that you never end up before a grand jury. It operates behind closed doors. You cannot read a transcript of proceedings. You have no right to counsel and no protection from self-incrimination. You may be compelled to testify and compelled to produce documents. And judges do not run the show; most of the time, prosecutors do.
The running joke is that they would indict a ham sandwich if a prosecutor wanted to. A wrongdoer will also walk free of the prosecutor wants that, too. (Remember, prosecutors rely on election campaigns for their job; that is often a good incentive not to prosecute someone.)
As to plea bargaining, bullshit... every legal system has that to some extent.
The "extent" being that its scope is limited to the point where it can't be used as a tool of coercion.
The point I'm making is that being that the US has democracy as a theoretical tool to curb malfeasance by people who wield the power of the government, but in practice it doesn't seem to work; either electors don't care, or they are persuaded to care about things which are not relevant. Australia, instead, has laws.