Arrow Season 6 Finale Synopsis Promises an ‘Epic Final Battl

I blame the timid approach to the first season.

They weren't sure how well the more "comic-booky" items would be taken, so they muted them. Plus they had the more "grounded" Dark Knight universe as their jumping off point.

Not Green Arrow, but The Hood.  Not Star City, but Starling City.  Not Dinah Lance, but Laurel Lance.
Laurel was a Lawyer and a spurned ex-love interest.  They never quite knew what to do with her since they weren't embracing the comics, so she just ended up as a standard, bland "She can never know my secret" character.  They tried a million other things to make her more interesting, (drinking problem, etc.) but they always had to build on that flawed base.

The show was dragging and kinda dull, and then in came Felicity who added a spark of life to the show, which it needed.  But then, she became the more interesting female character.  (And hate on Olicity all you like, but everyone admits that she was vital to the show finding it's footing in the early seasons.)  Then, in the second season, with the rousing success of the Marvel Films (Avengers came out the same year and cemented that the audience was there for true comic book entertainment) they started dipping their toe into that by introducing Black Canary, but obviously a more "realistic" version.  Laurel wasn't the right character to be her yet, so in came Sarah, and Caity Lotz simply OWNED it.

So now they were stuck with Felicity carrying the "personality" of the show, Thea as the rebel, and Sarah as the (ostensibly) perfect Black Canary.  Leaving Laurel with little to do narratively.

Now they have Dinah, who is probably the closest they have gotten to the comics Black Canary...but she is much more on the periphery than Canary should be in a Green Arrow show.

It's true that it's convoluted, but it's the route they got drawn into.