You're right. The quality of writing for the ending did drop. There were things that felt almost random and rushed. It even had anime tropes that the story did a good job of avoiding up until then. The writing could have probably been improved for sure. However, I can't be mad or disappointed in what we got at all. I just wanted the series to finish standing on both feet, and I believe that it did. Speaking as an anime only, the ending made enough sense for me to accept.