The ending wasn't bad, it was always going to be one of Ruth or Byrdes family getting killed, and the writers went for Ruth because her killing Javi was never a smart move, it was always going to get her. Story wise, I expected that ending, bad and rich always win, and you can't hope anything will happen with cartel.
What they did absolutely wrong were the characters and their behaviour, oh man that was really bad;
- Wendy is one of the biggest bitches in the history of TV, and the actress is playing her perfectly. However, she wanted to kill Ruth for entire last season or more, and then she was the one hrieven for her the most after Camila wanted to kill her, totally unbeliveable stuff
- Marty acted like she was his daughter for the entire show, and then decided to do nothing for her after the boat scene.
- as someone said above, Jonah and Charlotte going from good to bad to good in one day was terrible.
- Ruth convincing their grandpa with a gun to not bring the kids with them, and kids watching it and being totally fine with Ruth after that
They did nothing with the Priest though, and he could always be a danger to Camila, and I am not sure he liked Marty, and especially Wendy either, so that could haunt all of them later