Why build critical strike to double your damage, when you can build penetration to deal true damage?

Flat penetration (some examples ) is great if your targets have low Armor/MR.

Percent penetration (some examples /) is great against targets with lots of bonus Armor/MR.

implying that true damage is inherently better than more damage

Technically it's not actually true damage. You're just taking the maximum value of the ability.

It is what happens when you make marksmen more reliant on abilities then right clicking.