It's the same catastrophic evil, but there's a huge difference between the Throat of the Abyss and the Beast of the Herd. The Beast of the Herd possesses an extraordinarily fearsome power for widespread destruction, and this power transfers and spreads further as creatures move, like a plague that can never be completely burned away.
Bologue has already glimpsed that horrifying power within the Abandoned Land. All life was consumed to extinction, leaving only barren, nutrient-less stones.
The Throat of the Abyss doesn't have such direct destructive power, but in curved path shuttling, it holds an exceptionally strategic prowess, like a cunning assassin that slithers freely between pathways, leading troops in surprise attacks everywhere.
The difference in power has shaped two entirely different combat styles of calamity, also leading to the current retreat of the Throat of the Abyss... To it, this isn't an escape at all, just a habit of tactical relocation.
