If <i> means something different from <em>, you can keep them distinct while keeping everything "semantic". In fact, you could have a dozen different HTML elements for each use case of italics, e.g. <foreign> for foreign words and <t> for titles of books and movies, and it will be a mess, but it will still be "semantic". So the semantic-vs-presentational argument doesn't even apply here.

Meanwhile, the whole concept of using italics for emphasis is a Western idea. CJK languages, for example, don't use italics for emphasis, and most of their italic fonts actually look terrible on screen.