When the argument is "Superman would never kill Zod"
...and the response is "Superman has already killed Zod twice before"
That's not a tu quoque fallacy, that's a double fact. Very sloppy, sl4ppy.
Huh? Neither of those are the arguments.
The authors arguments are:
1) This Superman Destroyed An American City!
2) This Superman Was Reckless!
3) They Made This Superman A Murderer!
4) This Superman Movie Is Too Dark!
To which every response is (basically) "some other character does this, so it's okay here." That is the very definition of tu quoque.
...as a parting note and personal opinion, MOS was terrible because `Supes as a character is, frankly, boring.