Why is this a YMMV trope?

Would Alternate Character Interpretation be considered In Universe (or something similar that isn't YMMV) if the work with the different interpretation is based upon something else? For example, a Fan Fic interpreting a normally Silent Protagonist as a Cloud Cuckoo Lander?

Edit: Same question applies to tropes like Ron The Death Eater and Character Exaggeration, etc that are fairly subjective about whether or not a canon work has changed established characterization; would a fanon work doing it on clearly on purpose be considered objective?

Shouldn't the real life folder be moved to the file other? there's a reallife folder in there.

some of the examples of this trope I just don't get, Complete Monster is another YMMV trope so I'll let that one slide. but where did some of the My Little Pony Friendship Is Magic fandom get "Tyrant Celestia" or "Genius Ditz Snails" from? when has Princess Celestia shown signs of true villainy or when has Snails been shown to be anything other than a Ralph Wiggum?