It's not a violation of the law in any state to offer rent deals or incentives to new tenants. New Jersey has no rent control statute.

You didn't feel that the rent increase was shocking to the conscience when you agreed to it, and it's apparently the same deal offered to everybody else. Being angry that new tenants are getting a better deal, or that you might have been able to negotiate a better deal had you tried, isn't a basis for avoiding the rent amount you agreed to pay.