If the specific misconduct they got caught for netted them $x, and they got fined for $5x, who cares how much % of their global revenue is? That specific crime was still a net negative for them. I'm not sure why conglomerates should be punished more harshly just because they have more revenue overall.
Personally I think that C levels should automatically be disbarred if the corporation is found guilty of criminality as that puts responsibility on the people with the power to prevent it.
As for "who cares about %": every one who understands that fines that cost a company nothing, do nothing, all they say is "it'll cost you a trivial amount more to do this", turning what should be an instrument to rein in companies into simple monetary transaction that just goes on the books as an entirely expected and affordable expense.
It should be a crime, and they should have been found guilty in court over that, and the fine should be such that no matter your company's size, you can't risk running afoul of the law repeatedly. But it absolutely isn't.
While you thought you presented an argument against hefty fines, you actually gave the perfect reason for why they should be hefty. If illegal practices are affordable, they're not illegal. They're just the price of doing business. So make them hurt.