I'm pretty sure that's actually true in IO-land. At the same level fire gets Blaze and Blazing Bolt, Sonic gets Siren's Song and Screech. Even in "IO-land," there's no damage procs in stun or sleep, which are the only procs that Sonic Attack would have access to over Fire blast. Shockwave vs. Rain of Fire, RoF does 3x the damage at base. Fire ball vs. Howl, Fire Ball out damages it while also having less than half the cast time. If you're talking proc builds, you're looking at Ice and Dark and maybe Beam to compare to, not Sonic to Fire.
Adding a IO set dedicated to Sonic Blast would not fundamentally fix the issues with Sonic Blast, it'd just make it so you have less options in the world of IOs because either: that set would be so good for it, you'd be a fool not to slot it, or it'd be a middle of the road set, in which case, why bother altering a build composition just for it? If the power set needs changing, changing the power set is how you do it, not through slapping a dedicated IO set bandaid on it.