It's an OK personal theory, but I don't think it goes far even under the subtext label. Motivation = character, and BVS Lex is whatever his explicit motives are. What the film leaves out, he is not. If the film had wanted it understood that an impending invasion was key in Lex's rationale to make a 3rd-act-must-have monster he could've ended up not even needing, they would've made it explicit and integral to the rest of the story, as it would've helped provide a meatier angle. That's not where they went, though. It requires people to fill the gaps w the logic that's missing.
Exactly. It's a theory. My post was in support of a theory, pointing out that there's some hints in the film that could support that reading. There's not NOTHING. The idea doesn't totally come out of thin air. No one ever said those hints make it a FACT or that it's EXPLICITLY in the movie, just that it's something that could have been a factor.
As for why Lex created Doomsday when it was dangerous, it doesn't have to be so complicated. He did it because he wanted to destroy Superman in body and in legacy, because his childhood abuse taught him to despise fantastical saviors as frauds and to put his faith in himself above all else. That is the motivation. Doomsday is just one of the methods he develops to achieve his goal. Accordingly, his core motivation is explicit and coherent throughout the film; the method just changes in response to aspects of the plan failing or succeeding. Doomsday is the extreme response, and it's not unlike other extreme responses in reality and fiction.
Historically, governments have developed dangerous weapons that could have disastrous implications, like the atomic bomb, to make themselves feel powerful and secure. In fiction, you have rival governments like the USA and USSR daring to open a portal to another world (the Upside Down) in
Stranger Things when either they didn't know what they could find or did and persisted anyway. In the MCU, S.H.I.E.L.D. messes with the Tesseract at the start of
Avengers, instigating the threat the team faces in the film. They even dare utilize Hulk when they aren't sure he can control himself. Then we have Tony Stark, who in this very thread was recently touted as an ideal model for Luthor. He, like Lex in BvS, becomes desperate enough to create Ultron in response to an existential threat and crisis. Even Lex himself has created creatures like Bizarro and Nuclear Man in other incarnations in his quest to challenge the man of steel.
The creation of Doomsday fits with Luthor's motivation to destroy Superman (destroy god and faith in god) and his hubris (he believes he can control him or handle the fallout). Switching your focus and this thread's focus to Doomsday when your original point had nothing to do with Doomsday and wrongly claimed that Lex hated Superman because he reminded him of his abusive father does little to undermine the way that core motivation was presented in the film and, in light of the analogous scenarios I presented in the paragraph above, even the complaint about Doomsday becomes little more than a weak nitpick.
