So I created a custom sov that is not krax with defensive trait and the starting spearmen start with a staff instead of spears. Tried combining defensive trait with warrior trait and still start with staff instead of spear. If creating a custom sov without the defensive trait, I get spearmen that start with a spear. If I create a custom krax sov or use Kraxis, I start with Spikes of Krax instead of spearmen and they use a short spear.

It looks like the defensive trait on a non krax sov downgrades the spearmen's starting weapon to a staff because it does not use the short spear instead.

Seeing this happening I checked great hammer trait. If you start as Markin or start a custom sov as Gilden with the great hammer trait, your Militia unit starts with a war club instead of a club. If you use a custom sov that is not Gilden with the great hammer trait, your Militia unit starts with a club.