"Do you people across the water truly expect an actor to capture the cadences and nuances and accents of a language they studied after they were adult?"

Mind speaking in accents is one fo the skills in being an actor. And it is not as if the suggestion was that the accent sounded more Northumbrian than Yorkshire or something like that. The suggestion was that it didn't even really sound altogether English. So in reality when Crowe was being questioned over his accent sounding Irish - then it was that aspect of his skill as an actor that was being questioned. Hence the hissy fit. If an actor can't get an accent at least nearly accurate then (and I know this is only relevant in the land of the supposed accent) in a way they would be better casting an Englishman or just not bother trying what you haven't got the skill to do and just speak in a your own accent.