While I'd love a percentage based fee, this is a damages suit, so it should be actual damages these people are owed, as determined by the court. A percentage just doesn't make sense here unless punitive damages were also on the table.
In principle I agree, though, breaking the law should not be an affordable "cost of doing business".
“As you can see your honor, we actually lost 400 million last year. Negative profit. It looks like you actually owe us money when you calculate the proposed fine...”