Firstly, as @NicoProducto pointed out, this is duplicating discussion. You can see my general response to this idea over there - Change the use of OP tokens from a governance token to the main network token for gas payment - #13 by MinimalGravitas
As for:
This is impossible. Fees collected on Optimism are used directly to pay for writing to Ethereum mainnet. If you charge less fees there just wont be enough OP to sell for the ether the rollup needs to post it’s proofs. The fees aren’t arbitrary.
It would also destroy Ethereum equivalence, which is one of the main reasons that Optimism stands out against other optimistic rollups.