As someone who actually worked check in, I can say that yes it is more efficient to have the keys by the rooms. Doesn't matter if I get the keys while you are filing out paper work, etc. If something is wrong, the keys aren't where they are supposed to be, the wrong keys or even no keys at all, it takes time to fix. All of that is eliminated with the keys at the door. They have time to check to make sure each keys has the right status, etc. I have ran into every situation you can think of to hold up check in. The chain of command on the keys is exactly the same on board on done at check in. Actually less with them being delivered to the doors. They are printed the night before, by the guest service staff. Given to the stewards supervisor, already sorted and ready for the next day. Then just added to mail boxes. The old process started the same then the box is handed to someone allowed to go on shore and then given to the shore side team for which 40 agents now have access to. They were not sorted by room type or loyalty ADA. Only by name.
I worked for RC when they had a separate checking for suites and Ada guests. We had to walk across the enter room to get the keys for each passenger. So you saved standing in the long main line but took and extra 5 minutes of waiting for they keys.
Doesn't matter to me either way but I wanted to chime in from another perspective.