We’ve done a number of cruises using the Port of Miami, followed by a WDW stay. Always just the two of us traveling. We’ve picked up a rental car at the airport, driven to WDW and dropped it off at the Car Care Center at WDW. That supports Alamo-Enterprise-National. Typical cost for the rental has been less than $100 including gas and tolls plus the cost of getting from the port to the car rental center if we chose to use ride share rather than a shuttle. Rentals from WDW to cruise port would work similarly, in my opinion. I would expect the situation to be similar in Port Everglades except for being a shorter drive and car rental drop off at the airport would not have a shuttle option. There is an Enterprise location near the port with a shuttle.
We prefer renting a car because it makes our luggage handling simpler. We usually cruise with two wheeled checked bags along with carry ons. At the airport, we either rent one of the hand luggage carts or use a porter. Managing the luggage for the train seems more challenging than simply putting it into the trunk of a car and unloading same at the other end.