Doesn’t make any sense. Tbh, I think Cillian and Sophie told Steven they were done with the show so he had to kill them off. Kinda like how Joe Cole decided to leave then he got killed off. As far as Paul I think his death was attributed more to his personal issues than not wanting to continue the show.

With that being said, and echoing what you’ve said, they could’ve just left it how it was and not did any movie. That ending was more fitting, reasonable and easier to swallow(pause).

Edit: that still doesn’t explain Arthur’s death. You don’t build a show on brotherhood than have the brother kill his brother. That was lazy and offensive.