Thersites clearly exists in the Iliad to voice the obvious, normal objection that Agamemnon is a greedy nutcase embarked on an incredibly dumb war who cares nothing for his people, & they should all just leave. Obviously it's a disclaimed perspective but it's there.
Olúfẹ́mi O. Táíwòone tendency that comes out about period films is the insistence that XYZ moral thought would not have occurred to anyone in the ancient world. to be sure there are moral innovations and changes but the existence of thorough dissatisfaction with the present moral order is not a modern phenomenon