Definitely not true.
We have rented from Alamo at least a dozen times in the last few years and always do the online check-in, add my wife as the second driver, print the paperwork and go straight to the garage when we arrive in Florida.
Online check-in is my favorite feature of an Alamo rental, I'll pay more just to have this option with Alamo.
FYI: it's usually best to use the online check-in when you are close to departure date (in case you have any changes or rate drops and you want to cancel and re-book).
Personally, the day before our flight, I check one last time to see if rates have dropped any further. Re-book if they have and then use the online check-in and print the paperwork.
When you arrive at MCO collect your luggage and head out to the parking garage.
Follow the Alamo signs and head to the aisle/size that you have booked.
Load up (keys are in the vehicle),
Drive to the exit gate,
Hand the attendant your check-in paperwork, drivers licence(s) and credit card you used when you checked in.
The attendant will verify all the info, scan the vehicle out and hand you a receipt.
The gate will open and you are on your way.
Enjoy your vacation!