Yours is the superior porn-icon Contrary to popular fandom belief, I'm afraid threesomes are not the solution to everything.
WHAT? But the mathematics are so pure! Having sex fixes everything from rape trauma to maiming, so it stands to reason that having sex with twice as many people would cure what ails you twice as fast.
but I've never seen a man and woman paired who clearly have no authentic interest in each other and all the tension is directed at a female voyeur.
Well, Dick's too much of a wolf not to be at least a little interested in Dinah and Dinah definitely has noticed Dick (she did jokingly ask Barbara to set her up with him in the Dixon years), so there could be a level of Dick/Helena-type attraction there, with Dick's repressed(?) perchant for casual sex being justified by the Barbara connection. And if Dinah went for Ra's almost sight unseen, then going for Dick would be perfectly natural.
And I actually do recall writing a PWP that was Dick/Dinah with Barbara listening in (with their consent) and generally being the driving force behind the action, to the point where Dick's... interest... flagged when she was called away. I remember it because twtd gave it a rec that was basically "I know it's not femslash, but OMGHOT" :). Don't know if it counts because they're flirting and stealing kisses before Barbara's in the picture, but it seemed to work for my readers.