Pretty sure the writers didn't plan or intend on having Luna have a big role for the episode. It's more that they wanted to have a comedic gag of some sort because they prefer using comedic gags as a way to boost up people to like episodes. I rather not read a fanfic that "fixes" people's issues because it comes more forced than the original product. Plus, this isn't a new thing because it's typical for Luna fanboys to complain and whine by "changing up" Luna like with Garage Banned for example.