Let The Flash deal with all the superpowered crazies; Arrow is at its best when it’s on the streets dealing with more grounded threats like Slade Wilson.
The inclusion of Damien Darhk and the supernatural makes sense on paper, given that the Arrowverse became a whole lot less grounded with The Flash and Legends of Tomorrow.
But despite the natural charm Neal McDonough brought to the role, Darhk wasn’t the right villain for the show, and it never made sense that Green Arrow — a guy who’s best at shooting arrows that sometimes explode — could beat someone who was essentially immortal.