Often, around this time in southern India, kings would accept vassalage rather than annexation. In fact, in some ways, it's similar to premodern Indochina and the Mandala system, where regional hegemons would accept fealty and tribute from peripheral areas rather than outright annexing them, simply because it was easier than setting up local bureaucracy. While not exactly equivalent, this is similar.
Regardless, the Pandyas will have some conquering done before the end of Sundara Pandyan's reign, I can promise you that.
As for salting, I'd argue that in many cases it's a form of psychological warfare; not just to make sure nothing will grow in the area, but instead to send a message that "X conquering state will not be f*cked with." At the very least, it serves this purpose here. Plus, he's looking to cripple the Ganga state as well as subordinate them to make sure they can't rise up later.
Regardless, the Pandyas will have some conquering done before the end of Sundara Pandyan's reign, I can promise you that.
As for salting, I'd argue that in many cases it's a form of psychological warfare; not just to make sure nothing will grow in the area, but instead to send a message that "X conquering state will not be f*cked with." At the very least, it serves this purpose here. Plus, he's looking to cripple the Ganga state as well as subordinate them to make sure they can't rise up later.