You have 3 seconds (not 1/3 of a second). A torp isn't like an Aurora. It has no shields, no armor, 1 shot it's down.They are currently 980 m/second, laughably slow, since both my Carrack and my Star Runner can simply run away from them. (As can a Hammerhead.) Which means they cross the engagement range of those size 3 point defense turrets of the Perseus in less than a third of a second. They should be travelling at roughly 1800 m/s. (Roughly 150% of the maximum speed of the fastest designed targets.
To the front and off either beam there is only one turret that can engage the torps. (The bottom turret can only fire to the rear.)
If the torps are coming in one at a time, sure, you can probably get a majority of them, but unless you are facing a lone Eclipse, why would you only be facing one torpedo at a time? The Tali and the Polaris each have four rails.
Since a Hammerhead has size 4 guns, and there are few angles that a Hammerhead can't put 4 turrets on, it get significantly tougher to score a hit with a Torp.
And did you forget those S7 8k range guns? There any reasons why they can't be used to shoot down all the S9+ missiles well before they get to 3k range?