Why initial numbers need not reach the decisive battle

Does the Persian defeat against the Greeks show that larger numbers need not win?

The later battle is described as much more evenly matched after delay, attrition, and logistical problems reduced the Persian force.

An initial numerical advantage can shrink before the decisive encounter. In this comparison, the Persians win the first battle with overwhelming numbers. Delays, losses, and logistical difficulties then reduce the force available for the next battle. The distinction is between the size of an invading army and the troops it can actually bring into action; the two battles are not named here.