Hasn't Lex on his own already beat Superman multiple times? I'm not talking about keeping him utterly beaten, I mean physically knocked him out or incapacitated him.
Hasn't Lex fought Superman straight-up with his battle-suit? This makes no sense. Superman ain't no Sentry. Also, let me know where in the OP, Doom is fending off Wonderman, Ares, Wasp, Spiderwoman, etc. and is distracted. Because the first time Sentry bumrushed Doom, Doom messed Sentry up with his magic and was asked to relent by Stark. I don't think Superman is going to fare any better with that spell or have Tony Stark around to stop him. Lex has no chance against Superman in his suit? That sounds dumb.
Doom did bfr-self from the battlefield to summon the Mindless ones and was in his castle surrounded by all his tech, he can't do this in this battle.
Given how fast and hard Doom has been put down by herald level fighters, I don't think Doom's magic will be that much of an advantage compared with Superman's speed and strength. Superman is not weak to magic per se, just not strong against it, so if Namor can break the Crimson Bands of Cyttorrak, Kal certainly will too.
Lex might beat Superman -or be instrumental in his defeat- depending on how CISy the battle is.
He self-BFR'ed to be tutored by Morgan le Fay to do that. Now he knows how to do it. Why would he BFR himself again to learn it again? Given how stalwart his shields and armor has held up against Herald-level characters and beyond, I don't think your conclusion makes much sense. Superman gets waylaid by magic in ways other characters do not. That's a weakness. Let's not pretend otherwise. And there were circumstances behind Namor breaking the Crimson Bands of Cytorrak. Kal ain't breaking them.
This is my point. Lex hangs with Superman. And he's got the tools to put him down. Now he has a formidable ally. Deflection. Superman gets waylaid by magic or is hindered by magic far more often than not. Faustus has put him down twice through simple teleportation spells. He's been hypnotized by vampires. There is no established, arbitrary level of magic required to hinder, hurt and overcome Superman. And I'm not going to entertain your attempt to corral this conversation into such a pointless endeavor.
It's a game changer against Superman. And it's in the hands of a duo that makes advantage of three of Superman's weaknesses, red sunlight, (various forms of) kryptonite and magic.
Yeah, "magic doesn't autowin against Supes" is a pointless endevour in this fight
Superman hits harder, flies faster and has enough tools to work around both. Thankfully for team Kal holds back a lot. With enough CIS team gets some hard earned wins.
Nor Lex nor Doom casually work around people on Kal's level.