Two points to consider:
1) The SRM is a dedicated crit-seeker, while the ATM damage is split in 5 point groups
2) The SRM standard rack can use specialized ammo, e.g. infernoes vs. BA/vehicles and frag vs. infantry
For raw damage the SRM will also be superior ton by ton compared to an ATM launcher.
If you play only vs. mechs, then yes, SRMs could be easily replaced by SSRM and/or ATMs.
If you play in a rich and colourfuil universe, using all types of combatants and options like fire and smoke, the SRM will remain as a valid weapon choice.