I actually had to grind 14 Faith to be able to use the Astora's Straight Sword. I was super disappointed when my attacks were doing 29 damage with R1. I have a Drake Sword that does 200 damage per hit.
The issue isn't so much with the Astora's sword, but the Drake sword.
You need more than faith for the sword, since it will have other stats for scaling, but I recommend the above article so you build your character properly for the late game.