I always wonder how people come to the conclusion that AC is "mediocre" or "among the worst airlines".

Is AC service perfect? Of course not. But having flown nearly all *A and OW airlines I've found AC to be substantially better than its NA peers and as good as or better than most airlines in Europe, South America, Africa and Oceania.

Only a handful of Asian airlines (and maybe NZ) have consistently provided better service (at least in the air, not so much on the ground), and most people will probably agree that AC on average can't compete with SQ/CX/etc. - though some people may prefer the labour laws and work environment in Canada, even if those result in inferior service.