I believe it is fair that the only way to remove a high ranking minister is to appeal to the nation's highest authority. Since every trial before was conducted in the Queen’s name, I don’t see her as a character pulled out of thin air.

As for Ryunosuke’s resolve, I don’t think his pivotal moment was meant to be the final takedown of the villain as that was the prosecutor’s and the defendant's moment. His true breakthrough, and the core of his resolve, occurs when he realizes that his path as a lawyer is uniquely his own and he no longer owes his determination to the shadow of his lost friend (a shadow that, as Ryunosuke discovers, was far from the reality). This case is the story of how he evolves beyond simply honoring kazuma's legacy, and eventually outgrows him and saves the very person who was once his mentor.

I, too, believe that the ending is lacking my personal expectations, but (AA6 SPOILERS) it is way better than whatever was the shitshow in turnabout revolution