Doesn't SMART system happens to be a better substitute for torpedoes?
No
SMART is itself a torpedo delivery platform , so it cannot substitute a torpedo . Without its torpedo payload , it is no longer a anti submarine weapon.
Unrelated
As I see it SMART is a weapon system of the future , SMART will be a system within a plethora of weapon systems which will feed off various kinds of air land underwater sensor etc.
SMART will need to access considerable real time information from various sensors inorder to fulfill its missions with a high probability of success.
Given the costs, I believe the associated kill chain of SMART will not be standalone but a part of the kill chain of the INs system of systems which is being put into place slowly but surely.
SMART and importantly the system's which will enable SMART ( including other weapon systems etc ) will need time to come into place .
So SMART is a weapon of the future , not only because of the characteristics of the weapon but because of the sensors needed ( space , air , underwater ) to put it into effective use.