Two weapon fighting clarification

By Somnium2, in Black Crusade Rules Questions

Would a CSM character fighting with the typical combination of weapons (chainsword-bolt pistol), have to get both two weapons wielder traits (both melee and ballistic) in order to be rid of the penalties?

It seems a little unreasonable, having to pay for both, while one could be just as lethal (if not more) wielding, for example, two melee weapons and only having bought one trait.

That is the case. You have to get both, and then purchase "Sidearm" to negate the last part of the bonuses.

Space marines are also Ambidextrous, which would lower it to -10 starting off using two weapons to attack.
so while they may have to buy those two in order to use two weapon fighting
normal Humies have to buy ambidextrous and the talents

somnium said:

Would a CSM character fighting with the typical combination of weapons (chainsword-bolt pistol), have to get both two weapons wielder traits (both melee and ballistic) in order to be rid of the penalties?

It seems a little unreasonable, having to pay for both, while one could be just as lethal (if not more) wielding, for example, two melee weapons and only having bought one trait.

That's only partially right. The Two Weapon Wielder traits aren't needed to negate penalties, they're needed to attack with both weapons at once, and ISTR that the rules *do* say that you only need one of those traits to attack with a sword and pistol in the same turn.

So you can get your penalties down to -10/-10 with only Ambidextrous and one TWW trait, it's only Sidearm that requires you to buy both.