Sorry to hear that you were so disappointed.

I will admit that I did see a lot of the elevator and buffet table issues on the last day. We pretty much took the stairs everywhere we went anyway. When we took an elevator we made sure that it was an aft or forward one since they were not as busy. DD6 and I waited about 10 minutes for a table on the Sea Day breakfast buffet before we just took our trays down to our cabin and ate there. I think that a lot of the issues were due to it being too cold to go outside on the last day.
We anticipating all the days to be as cold as the last day, so Nassau and
Castaway Cay weather were a nice surprise to us.
That being said, we liked the rest enough that we booked again. Even if you choose not to do a
DCL cruise again, I think that was a really nice thing for you to take your granddaughter on a trip like this. I do not think that many of us have grandparents that would do that. In the end she probably won't remember the lines or rude people, but that her grandmother loves her enough to spend special time with her.
On a side note, how did you like the HA cabin?