User blog comment:TheDoctor230/Season Coincedences Arrow/@comment-24152851-20170116062314

They do seem to let main characters die a lot. It's to keep the show's dark tone, and that Oliver does not always get happy endings.

A superhero leaving the show might not be their intentional. Sometimes the actor is unable to keep commitments to CW and depart.

Season 4 did break the trend a bit since Damien Darhk didn't know Oliver personally until after he encountered his superhero alter-ego, and took a lo whereas everyone prior to that had personal involvement with Oliver Queen himself. Even Prometheus seems to know Oliver is the Green Arrow from way back.

Well of course the main bad guy is the leader of a group. The only way an Arrow villain can make he's not just a "villain of the week", is if he's at the top of an organization so he can keep sending minions for Team Arrow to deal with, while not coming to harm himself. If they do get defeated and captured, their minions will soon break them out of custody so they can keep harassing Oliver until the finale.

"at least 1 person joins team arrow" - I think this is more a coincidence. They've had the core team for a very long time, and most of the new additions to the team were main non-action characters that got promoted. Season 5 had a massive change with the new recruits replacing the core team.