In my own personal opinion as an artist, the pre 2013 Stella looked too ''ideal'' aesthetically (Noctis too). Slim cheeks, small chin, narrow face; it was just too visually perfect, much like out of a manga. 2013 Stella changed to a more round softer visual where she appeared more human. Post 2013, personally Luna looked like she was combined with Stella from 2013 and before. With the round natural features but also combining the features from pre-2013. But visually the nose was too small defined, chin was too long, mouth was undefined, eyes slanted, it had a weird balance.
Personally I think it was a good choice to go back a step. 2013 Stella may look ideal in the sense of appearing cute, but it had the right visual balance.