Roman Legions seem too weak

[Dayve]

You must be joking... I conquered half of Iberia in the Camillian era using a few native Roman troops as a core surrounded by hordes of allied Iberian light spearmen and light swordsmen and generals who barely scratched 1 command star. I conquered the other half in the Polybian era with much the same legions and never even suffered 1 defeat.

You must be playing on hard or medium battle difficulty. However i will agree that Roman troops take way too many casualties against javelins, even non-AP ones hurt hard. You get 1 unit (or nightmare situation, more than 1 unit) throwing javelins at your Roman heavy infantry and large full bodied shields be damned you will take 50% casualties in that unit, especially the Camillian and Polybian units, 1 volley of javelins and your hastati are decorating the ground in the hundreds with their blood.

[Tellos Athenaios]

Well that's the Romans for you: they use light infantry to take the bulk of the casualties-- and if things turn less than pretty that way they'll send in another 10.000 of them.

Mind you based on their equipment you shouldn't even bother with placing the Hastati for your first line. You take a shorter, slightly curved line of Principes, and keep a longer curved line of Hastati behind them. The main part of those Hastati rush in just before the enemy infantry engages. Rear guard are the Triarii and you move them in when enemy cavalry engages your flanks.

This way you should have less casualties inflicted by enemy missiles.