Torps are a 1shot weapon that roll 4 dice. On a basic x-wing, that is 1additional die. However, they eat up your target lock. So, by the math, that's 2 hits on average. But a target lock with your basic 3 dice is 2 and 1/4 hits. Other than not getting the extra defense roll at range 3, where is the advantage for the extra points you are spending? Even if you spend another turn and get focus, that only raises the number of hits to the 2 and a half. Thats not much better than the regular attack.
What am I missing?