You're still making the mistake that legal personhood is literally being a person. People can go to prison. Abstract concepts cannot.
(Or get rid of prison for natural persons, I'm on board with that.)
Corporations already have the rights of people, because when corporations do crimes, the corporation, and not the people who constitute the corporation, is held legally responsible. What we are objecting to is that corporations are exempt from forms of punishment that are applied to natural persons. Either figure out how to make the punishment apply to corporations, remove that form of punishment from consideration for natural persons, or ignore the corporation for legal purposes and punish the humans behind the abstraction layer. It's pretty straightforward.