Not sure where the complaint should go or whether it will be heard, but *G should receive priority boarding on ALL *A member airlines. That's a published benefit per *A website.
LAX
Was sent on this routing to follow up on a complaint from some of our German engineers (LH elites) who had complained about non-priority boarding on CO. Found it to be true. Was a factor in our decision to remove the new UA from our preferred carrier list. OBE when the new UA had such tremendous operational issues post 3/3 that our company forbid booking with UA.
Agree it's a violation, but in the scope of all that's not right in the world of our fellow domestic *A member, I don't think it's a priority. Did contact someone in customer service at the * Alliance, but never heard back.