FWIW, two family members describe themselves as "slaves to UA" because their 40+ years of mileage/level make it difficult to leave, yet both regularly experience extreme rudeness and/or incompetence from GAs to Premier Club(?) gatekeepers. I haven't flown UA myself since an incident in the 90s when the two remaining employees at IAD closed up and left because it was 2300, stranding two elderly couples in wheelchairs. Our international flight had arrived five hours late, we all missed our connections. They took care of the first 50 or so pax and let the rest of us hang.
I don't fly AC regularly, but despite rumours otherwise have never experienced anything but classic Canadian politeness.