How did the 10 plagues demonstrate the ridiculousness of the Egyptian religion?

Several of the plagues were aimed directly against the Egyptian gods. They worshiped (among other things) the Nile; and the first two plagues showed that the Nile was under God's jurisdiction, not its own, and that it was a source of trouble and not only benefit.

The lice embarrassed Pharaoh's religious elders who were unable to replicate it through their sorcery.

The boils hit the religious Egyptian elders before afflicting the rest of Egypt.