Moving to LA will only be marginally more profitable for the Chargers than staying in SD. and that's only if they win. If they aren't good, their ratings will suck as will the outside revenues. It's one thing to suck as the only game in town. It's quite another to be fighting a hometown team for fans. It would taking being a consistent playoff for several years to even have more fans in LA than the Raiders.
By the way, I oppose any city building a stadium for an NFL team. The owners of NFL teams are usually opposed to welfare. Let them build their own stadiums. Spending hundreds of millions of dollars for a stadium the team will only use 8-12 times a year and won't be used for much else is stupid.
At least indoor arenas can be used for hockey, basketball and hundreds of other events every year.