Many scholars do not believe that the army of the Persians could be so huge. Why?

Nowadays, scientists are rather skeptical about the number of troops of antiquity. They argue that historians deliberately overestimated the number of armies in order to give meaning to these battles. The main arguments of scientists are as follows: in order to maintain an army of more than 100 thousand people, a huge baggage train is needed and a well-established supply system. In the conditions of that time, it would have been very difficult to gather and maintain such an army.