I don't know if it's occurred to anyone recently, that the real/biggest reason that Lex Luthor felt like an alien while growing up in Smallville wasn't just that he was extremely intelligent (to an admittedly astronomical degree), but mainly due to the fact that he was hypersensitive, struggled to connect with people unless he felt they were very similar to him and was basically socially inept, all likely due to a possibly undiagnosed neurological condition (your guess is as good as any).
I feel like it's been heavily implied for a while now in certain Superman works that Lex may have literally been on the autism spectrum or have grown up with a related condition. Combine that with super genius intellect, a deeply ingrained sense of superiority and entitlement as well as emotional growth-stunting abuse, and you have a recipe for the perfect completely unstable, super villain catastrophe.
Likewise, I think it's been implied for a while now that Clark is also a representation of what being neurodivergent is like, but with the metaphor being made actual. Hence why he doesn't "feel like" an alien. He IS an alien. An alien that has had to mask what makes him different from others his entire life. With only those closest to him knowing the truth.
A perfect example of both of these concepts can be found in the first issue of the (technically...) on-going Superman miniseries Superman: The Last Days of Lex Luthor. (Same with its spiritual predecessor Superman: Birthright, if I'm being honest.)
What does anybody else think? It seems to me that only a few people at most have talked about any of this before, at least online.