[Sir Francis Dashwood]

Denethor was the big city mayor under the spell of Sauron...

[Corin Stormhands]

Denethor was the big city mayor under the spell of Sauron...

Denethor was the Steward of the Kingdom of Gondor. Not the mayor. Not a big city.

Saruman was under the spell of Sauron. Denethor was weakened in his own quest for greatness.

But he was not under the spell of Sauron.

Have you read the books?