As for establishing an academy, Dias wouldn't have to be the instructor. His fame would be enough to attract specialists in each weapon discipline and they can be in charge of teaching. If you look at modern day universities and similar places, the head guy doesn't teach. His job would administrative rather than practical. Not that Dias would be particularly suited for that, but the impediment isn't his lack of fancy tactics and strategic understanding of the art of warfare. It's that Dias isn't going to be good at hobnobbing with the elites in fund raising and relationship building.