While I get your point, adcs do have their own skin line, this decision was down right flawed because its destroying the established "thematic" of this skin line:
Champions based after looking/relating to "Cupid":
Ashe has a love bow, and in the background Tyndamere is falling in love in the background, her visuals in game have been changed accordingly.
Varus, while not having much in the splash, heartbow, his visual look is designed based on how "Cupid" is a baby in a diaper with wings. His visuals in-game match Cupid.
Vayne is just as similar as Ashe, Heartbow, and her visuals have been changed accordingly.
These skins, or "skin line" fits the idea that these characters are just little cupid versions of themselves, which probably is what "Heartseeker" is supposed to mean or portray. But, everything changed when Orianna was added...(haha references)
Orianna, does NOT fit this thematic. She may have all the hearts, visuals, and probably splash art that makes it more believable that she could be a heartseeker but she just doesnt work here. The skin is admittedly well done, its pretty, smooth, well designed but its real name should be: Sweetheart Orianna. Orianna just doesnt feel right for this, she lacks a bow, she lacks the looks, and shes really designed more cutely rather than ...."open" like the other heartseeker skins. Its hard to explain but it just doesnt feel right that she is getting this skin for this skin line, it feels like it was just a last second change because they realized that they had made two sweetheart skins and forgot to make a Heartseeker one.
Sure, ADCs shouldnt get all their own skin lines, but that isnt an excuse to throw random champions in and break their original formula for the skin line. (Lets be serious, that whole "Not all adcs w/ bows have to be in this line" excuse was made up on the spot)