The added range and them being inf type is the big difference if compared to Shatterers, Snipers can kill Mutant marauders and Grenadiers from afar while Shatterer might be more fragile to these. Also it's an option for barracks openers, while Shatterer is for vehicle users.
That's like saying chem warrior is useless because there are chem buggies. They are two different types of units with the same damage output.
Long story short, tehy work as intended.
However, a minor buff to snipers could be to give them scout visibility, make them actually spot 3 squares around themselves, similar to drones and dogs.