There's also the fact that training somebody to be an archer takes waaaay longer than teaching them to stand in a line and fire a musket. Plus bayonets = bad time for horsies.

The outdated army trait seems to refer to more outdated gunpowder weapons, like wheel locks and such. To be all 'lolmyoutdatedarmypwnsyermodernone' kinda destroys the entire point of it existing.