1) slavery and ownership of lives: they could literally own slaves. No matter how much anyone will want to twist "working for corporate" as slavery, there is simply no comparison to such direct dominion.
2) magisterial power: consuls and praetors could even sentence people to death with barely any resistance. You're welcome to find me an example in the first world.
3) land and resource control: we are in an era where the masses have a much larger share of land and resource ownership compared to then (e.g: latifundia).
4) judicial immunity: yeah, we all know the legal system isn't perfect but you don't have the same extreme levels of abuse you had back then unless again, you appeal to corrupt 3rd world countries.
5) military command: I don't see the billionaires in the first world with their own personal armies.