There was raw sewage in some areas. Lack of AC in cabins without a balcony made those cabins impossible to live in. At least one person broke her leg while trying to go to the bathroom in the dark.
It is more then just a crap vacation. There is no way that I would take a cruise with Carnival after being on that ship so a free cruise is a bogus offer. Maybe a refund twice the purchase price.
I get that you don't like cruises because of the amount that staff are paid and how they are treated but the conditions were worse then you are acknowledging.