The most important thing was that Heaven Rank powerhouses simply couldn't pass through the Planar Path. If a Heaven Rank powerhouse tried to do so, the Planar Path would collapse, and the connection between the two planes would be severed. This would make the Heaven Rank powerhouse fall in the endless void, dying without leaving a corpse behind.
And there was a limit to the quantity of people. If there was nothing unexpected, the Raging Flame Beastmen's side was filled with powerhouses and their numbers were roughly similar to the human side, while their strength wouldn't differ too much.
The Odin Kingdom and the Andlusa Kingdom's powerhouses more or less matched the Raging Flame Beastmen's powerhouses when added up. Even if they could suppress the Raging Flame Beastmen, their advantage wasn't that big.