It is definitely borderline OP. I don't think I have played any good player not using either Staravia, Rufflet, or Salamence. They're all key wall breakers and most often a teams MVP, or win condition, if you will. I run Rhydon on my main team, and Honedge on my other. Bulky Rock/Steel type is a role for only one mon on a Balance team, so I don't double up because I need resistances to other types. Anyway, birdspam teams always have an offensive water or ground type like Drilbur, Froakie, Staryu, Kyogre, etc. to deal with bird-walls.
The existence of tough rock or steel types doesn't make Birdspam bad because there is also a plentiful selection of Pokemon to remove them. Magnemite and MegaGar come to mind because they can trap, otherwise PKyogre and PDon, many more.
Also can someone explain why Rufflet is being suspected and not Staravia? I realize Hustle is the thing Rufflet has over Star, and that allows it (when it hits) to 2HKO the entire meta game, but Staravia can 2HKO about 85% of it too, is quite noticably faster, has priority, and Reckless which gets it closer to a power level. Star also runs a much more effective Scarf set. I think they are both equally OP, if not Star more so.