BA038_Passenger I had a talk with the person who I believe you communicated with on the day of your checkout. As I suspected this was an extraordinary situation, on the day of your checkout there was a large group that requested early check-in. I think regular guests who met her (myself included) can share opinion that she is trying to go above and beyond for customers. I believe she has discussed with you different possible options to handle the situation.
As for the Check-In experience I think you probably met a new or not very experienced person. It is their practice to pro-actively ask for Late Checkout and insisting on breakfast Diamond benefit is not usually the case. I advised her on your feedback, so I am sure this will be taken into account.