When Arrow grapple-hooks off into the sunset after its eighth and final season, the CW's small-screen DC Universe is going to be missing an essential darkness to balance out the sunniness from the likes of The Flash and Supergirl. Luckily, nobody broods like the Bat-family. Batwoman, developed by Caroline Dries and Greg Berlanti, finally brings the Arrowverse to Gotham City full-time after the glimpse we got in last year's "Elseworlds" crossover event. But thank Grodd, this isn't the origin story we've seen time after time after time. (On average I see Thomas …