I completely agree with your post, and your correction of the abnormal/pedantic neologism 'USian' (how would that even be pronounced? /juːʃaɪn/? /ju ɛs aɪn/?). It's not just English speakers who use the term 'American' --- I've frequently heard it in use by Polish and Hungarian people when speaking their own language: "[Polish words] American [more Polish]".