Tell that to the Spartans. Massive numerical advantage will always win out. All the defending force can do is delay.
To be fair the Spartans at Thermopylae were betrayed by Ephialtes, who led the Persian forces around the flank, via a little known mountain pass. They stood up valiantly to the frontal assault.
Thermopalae didnt have waves after waves of soldiers wilfully kebabing themselves on spears so the blokes behind them could climb over their corpses either to be fair, plus the Spartans didnt have to deal with their own dead being raised to fight against them.