I confirmed last year that Citi Professional card still carry primary car rental insurance.
I also remembered you can pay some extra for AMEX full car rental coverage. (You need to be careful that some people say "discount" code booking is not valid.)
With the Citi Prof card, there is a clause for the coverage, that is, your rental must be business-related. If the insurance company asks for proof, you better be able to provide such. Else, the claim will be denied. Unless you are willing to take the chance on a leisure trip, that the insurance company would not ask for proof.