Everything you write is pretty accurate, but you just don't quite get across how boring it was. I was actually kind of excited to see exactly how they were going to make this a musical and how Lady Gaga would end up fitting into that. Having the main characters occasionally stop all the momentum (such as there is, given the threadbare plot) to mumble their way through a dusty old standard was not what I was hoping to see. And it just made an already slow movie drag even more.
Say what you will about the first movie (it has a self-important air that it doesn't really earn, it wears its influences on its sleeve), I think it's rarely boring.
And yeah, the courtroom scenes were absolutely ridiculous. After how grounded these movies are in general having the judge allow Arthur to traipse around the courtroom like the southern bird lawyer in Futurama and do nothing but bully a witness took me all the way out of it.
And no, there's nothing on the screen to justify its ridiculous budget, nothing at all. As I said before even Gaga is just wasted. There's basically one big action set piece. 90% of the rest of the movie is the same prison interiors, the same courtroom. They deserve for this to be the bomb that it is. They had no business spending so much on a movie that looks so dull.
And, ok, I hated the ending, and part of what rankled me about it is that Todd Phillips changed the narrative to make a point to the toxic incels that revered Arthur in the first movie. There was never meant to be a Joker 2. The first movie was supposed to stand on its own and it definitely implied that Arthur would become the Joker. He changed the story as a "Take that" to the fans that made the first movie a hit. But couldn't he have gotten his point across without changing the intended story? How am I, who came into these movies as a fan of the character first and foremost, supposed to react to the fact that this was never the character I came to see, and that the only reason for this is that Phillips felt he needed to make a political point?
Sorry, WB, swing and a miss.