Gotham being corrupt should make it even easier for a billionaire like Wayne to control things, because as we see in real life, it doesn't take all that much money to influence politicians. There's nothing stopping Wayne from bribing the shit out of everyone to do non-evil things, then once Gotham is in a more stable place, bankroll campaigns for politicians that aren't corrupt. He could literally drain the swamp by backfilling it with money, but instead he decides to run around at night in his little gimp suit punching poor people