Pretty much agree with you here! It didn't even occur to me that the ending would be considered 'sexist' until I read that article just now. I thought it was pretty obvious that Princess Uni-Kitty et al were constructed by Finn, and that the deal with his sister wasn't that she's female but that she's obviously very young and that Duplos make adorable alien monster creatures.

And I am pretty tired of getting set up for an awesome Token Female Badass only to have that thrown away at the first opportunity and never seen again, for no real reason.