Fun fact : every civ's SO is unique

Siege Onager is for now the second least common tech in the game after paladin (until DE comes out), with 9 out of 31 civs having access to it.

What I find extremely interesting, and is a testament of how well designed the game, no two SO are identical in post imp. The combination of civ bonus, unique tech and tech availability makes each SO have different stats from another one. Here's how it breaks down :

Aztecs : trained 17% faster

Celts : trained 20% faster, fire 25% faster, +40% HP

Ethiopians : +0.5 blast radius

Koreans : -2 minimum range, +1 range

Malians : no Siege Engineers

Mongols : move 50% faster

Saracens : regular fully upgraded

Slavs : 15% cheaper

Teutons : resists conversion, +4 melee armor

I find it really great that with 31 civs we still manage to have a standard unit still be unique for each civ that has it. That's good game design.