I would say that your last paragraph is accurate. The lack of earlier boarding times (they are really check in times) stems from your late booking. You could only check in after you had booked the cruise, and by then, all of the "better", i.e., earlier times, were already gone. So you haven't really missed out on any secret knowledge. You are just a last minute booker who is now going to have to deal with the cards you have.
🙂