Missilesides with EWO aren't the greatest tank busters, true, but that's not the purpose of me taking them. I'm playing footslog heavy Tau, and they can't afford a single enemy unit playing around in their backfield with the threat of assault.
So when an opponent plays Ymgarl Genestealers, Sly Marbo, Drop Pod Marines, Scourgers, Snikrot + boyz, Sentinels, Warwalkers, etc..., the Missilesides are there to punch a serious hole into that unit.
Granted, the Missilesides don't have the amazing range of the railgun anymore. But a 30"/36" bubble of 24 shot Interceptor TL death is more than enough to defend the back field.
For true tank busting ability, I would need to rely on fusion guns and the Hammerhead.