I wonder how many times this happens on the cash side of things in relation to
DVC? I can tell you that we never got rooms late when paying cash At WDW or any other hotel I have stayed at.
I travel quite a bit and it happens a lot.
On the cash side of disney we've had it happen. For me, the online check in is huge perk along with magical express. I don't even have to go to the room after arriving in Florida, I can wherever I want and plan accordingly. To a certain extent, I'm surprised they don't make a direct to park magical express route.
Once bottleneck for DVC is the multiple room types. That leaves a pretty small pool relatively speaking to block a room for an arriving guest. Many hotels assign your room on check in, which allows the flexibility to put the guest in front of you in the first available clean room.
While disney can assign on arrival, they do pre-block rooms. They even have an option on your online check in to indicate it's more important to check in early/on time than to get your room request.
That being said, if they publish a time, they should be trying to hit it. That also means people need to be good about checking out on time, and letting the desk know you are out of the room....or even as you walk by the housekeeper in the hall as you go by let them know your room number and that it's empty.
If it's important to be in your room on time, call that in for a request, and expect to go to the desk when you arrive regardless of whether you received a text and let them know you are here and your preference above all else is to get into your room. While the rooms are pre-assigned, they can still move some around within the correct category. However, don't think that get you some sort of upgrade.
Disney does not have a surplus of housekeeping help, so don't expect the standard to improve much unless wages and conditions make it the best housekeeping job in the area. Those wages end up in our dues. So it's all intertwined. If they had the staff, they'd be doing daily housekeeping and forcing a charge for it down your throat.