Is attack rating stat completely useless with Faith as bow?

No, its still relevant.

can you explain a little. i'm confused as it says "ignore target defense"

itd only erases the ar/def factor of the chance-to-hit formula, so attacker lvl and defender lvl are still important. furthermore (and this is directly to your question), itd does not work against players, champion monsters, unique monsters, bosses. against all of these types, ar/def are relevant

thanks alot. I noticed that monsters are melting more with my gmb faith than with windforce, even though I have less dps. The ignore defense on normal mobs and increased ias are doing good.

With lvl 15 fana, how much ias should I be aiming for?

what setup are you using, so that windforce does more dmg than faith?

ias breakpoints
lvl12 fana: 8 24 50 99
lvl13 fana: 7 23 48 95
lvl14/15 fana: 6 22 46 92