^ yes, assuming that Mags is allowed to reform the armor to restrain them.
If the armor is intact and Magneto is just holding it in place while the hero tries to overcome the force of his hold, then the type of metal is irrelevant (although adamantium is actually pretty hard to magnetize isn't it? might just make it tougher for Magneto here)
^ Repelling and attracting adamantium seemed as easy as any metal. Has Magneto ever commented on how much harder adamantium is to reshape? I think it's in-character for Magneto to just create a thin shell & shackles with thorns that pierce each character's bodies the more they resist than anything.
It's easy for Superman to push/propel a negligible weight of adamantium 5 feet. It's much harder when you have a ferrokinetic resisting that attempt. It's much much harder when you have a ferrokinetic on the level of Magneto doing it. But if Magneto just spikes that crap through your body so that you'd have to tear through your own muscles and organs just to flinch, that's something I see few characters doing.
Iirc Claremont or Byrne clarified that adamantium is not magnetic but that Magneto can manipulate anything with an EM field. My (minor) point was just that Magneto could likely exert a relatively stronger hold over a suit of iron than a suit of adamantium.
As for the rest of your post, we agree, I think? This isn't about Superman vs the metal, but Superman (and the rest of the gauntlet) vs Magneto's hold on the metal. And, the thread stips favour Mags if Mags can get creative in the use of his powers to restrain.
The more narrow the meaning of "restrain", the more this is just a plain contest of strength (albeit physical strength vs tk) that favours the gauntlet.
^ It's an interesting scan and I definitely see where one can interpret it that way. The prior page gives more context. But I'm not sure targeted magnetism on those who are "made of metal or wearing way too much if it" isn't the reason other than adamantium simply not being magnetic. Maybe the computer knows not to target adamantium.
But thanks for reminding me of that scan. I'd completely forgotten about it.
^ I think one of the things you have to consider is that even if Magneto made a skin-tight sheath, the characters who can fly can propel themselves. So Magneto has to counteract that flight propulsion.
OP clearly stated that if the opponent moves 5 feet, it's a loss for Magneto.
Granted, none of the Marvel characters has flight except for Namor... and if his feet-wings are compromised, so is his flight. SO you're probably right that the Marvel side is easy.
But even with the DC side, I figured that Magneto would just spike these characters through their bodies so that any attempt at flight propulsion would only backfire. That's why, without phasing, Martian Manhunter has the best chance because he's physically malleable.
^ I didn't think about that. Unless Magneto knows to completely encase him, any of Lobo's blood that spills forth from restraints will result in a clone. And if those clones move 5 feet from Lobo's original position, then that is a loss per the OP.