The Casse generals are the worst generals in melee in the game, you just need to learn to use them as they're meant to be used: morale support,
running down the odd light cavalry, and a few extra javelins in the mass of enemies always helps.

I don't think anyone gets historical leaders. You might be lucky (or unlucky) enough to get a general like Caratacus, but generals are born or adopted or married as your version of history in your game plays out.