You can see every individual feather on this parrot mount, and even notches/splits in a great many of them. On Rexxar, you can see every ripple in his muscles, arm hair, tuft of fur, stitch on his leather bag & gear, crack/notch/crevice in the animal bones, every wrinkle on his face, the wrinkles in his elbow skin, layer & direction of leather wrappings on his boots. Even the rough, slightly eroding quality of his shoulder tattoos.. How in the world is that low-res? If you were trying to refer to polygon count, again I just ask you to look at the models, and even find their animations in the model viewer. Ever since WoD, WoW's models have phenomenally improved in all respects. Just compare that Rexxar to the original model. Or compare the old character models to the updated ones we have as of WoD.
Just because Blizzard choose to digitally paint their textures over rendering in graphics using some modern engine like what you see in every other game, does not mean WoW is low-res, or that Blizzard is "concocting an excuse". The painted-on, "cartoony" look is a unique aesthetic which draws from the game's old Warcraft 3 roots. As the graphics of this game have visibly improved since vanilla, that look has stayed consistent while looking better with every expansion as well. I'm pretty certain this what an artstyle is, and why pretty much everyone considers this look to be the game's artstyle.