I don’t know about Superman being an INFJ…perhaps he is more extroverted but forced to be an introvert so he isn’t accidentally discovered…I don’t think that was ever really explored in the comic books.
As for Lex Luther being an INTJ…I would most definitely place him more as an ENTJ.
Clark Kent could be an infj but Superman i'd say cannot be typed. If he can be typed then he reached the full potential for all functions ; meaning he can use all functions just cuz he can.lol
Clark feels like an ISFJ; the goodie two shoes, quiet, unassuming, but grounded and moral.
But Superman as an Ideal is PROBABLY ENFJ. The embodiment of everything good-- with the willingness to GET OUT AND DO IT.