Too much dumb stuff happened.

I ALMOST WATCHED THIS LAST NIGHT...I WATCHED FLIES FUCK ON CHANNEL ELEVEN INSTEAD.

You seem to be of a nitpick disposition. I just enjoyed the ride and didn't ask questions. Interesting concept, all in all a decent movie though not one I'll re-watch.

The wife didn’t know he’s the butcher. She saw that he often left at nights and returned smelled of cleaning fluid, and she saw him go to an abandoned building with just a chair, which she found strange. So she left the concert ticket receipt just to put the police on him. She merely wanted the police to look at her husband and then find out that he’s not the Butcher.

I agree with your points about pushing the girl and setting the bottles in fryer

I think the dumbest thing was the vendor knowing about the trap. The police would not have told him anything. Same with the singer. If the police had let her people know what they were doing, she would not have been there.

BTW: This is interesting if it's true. But it explains why the wife would not call the cops.
Supposedly Shamalayan may have had another twist in mind that was not included in the final product. The wife herself was also a serial killer. She realized who her husband was and that the police were getting close. She set her husband up so the police would catch him without implicating her. Because if they looked at her too closely, they might have caught her too.

As I said, don't know if it's true or just a fan-based story but might have been a heck of a twist.

and dón't forget the issue with that random woman (the "Karen one") and her daughter with Riley that doesn't get anywhere. At the end Riley goes up on stage to sing with Lady Raven (what a stupid name) and the woman and her daughter get angry?? And they start yell to each other?? And it ends there??
I thought it would be some kind of Riley arc where she gets to a point where she sends her "friends" and the mom to F themselves

- Why were the cops oblivious to everything happening inside the arena when there was a camera everywhere?
With thousands of people, you're not going to see everything and he did nothing that really stood out.

- If his wife knew he was the butcher, why continue to allow your child to be in the same house as him?
She suspected it. Plus, he's not killing their kids - it's a problem with the spouses of child molesters.

- The fat black worker was as dumb as a post.
He was friendly and trusting. How many people fell for Ted Bundy's broken arm routine?

- The cops were looking at the surveillance cameras and were able to determine who the killer was from that, but none of the cops who saw him face to face (including an entire room full of them) knew it was him.
Who said they saw him? They were using various descriptions.

- The cops said that he was going to create distractions but: they didn't look at the cameras when the girl was pushed and they didn't look at the cameras when he put the bottles in the fryer.
The old woman said a major distraction, like a fire alarm. A drunk tripping and a grease fire ain't that major.

Why didn't his wife go to the police when she figured he was the killer?
She hoped that she was wrong.