It seems that the script generates land from bottom to the top, but then the features are placed i.e. polar ice, that simply override it. You can clearly see that there is not much tundra and it ends abruptly.
Pre-GS there was a bit less ice I think, so less land was cut.
In GS it seems that devs simply added more ice, and forgot about adjusting the actual land, so it won't get cut.
Btw, is it a modded map or a standard one? Imho, that world doesn't look like a standard continents script.