It probably would take more, because Magneto is often written to be stupid as shit. I mean why in the hell has he never mugged Ultron? He could peel his shell off of him in a sneak attack, and use the adamantium as a new suit of armor. I'm basing this off of his performance against Wolverine, when he removed all of the adamantium from his body. Well that's what I would do if I was Magneto. He could literally have the physical strength of adamantium working for him like Spawns Necro Symbiote works for him sort of.
I think Marvel Earth would win this, as long as they acted fast enough before these guys fused into one, or made so many duplicates of themselves that it would take outside help to even the odds.
Oh yeah, well I'd creep up on him, and mug his ass if I was Mags. Seriously though Magneto would raise his tier ranking if he wore adamantium armor, and shaped it as he fought in close quarters. He'd be a beast.
Magneto can destroy anyone here who has metal on them so....everyone. Not sure about Ultron controlling the EM spectrum (honestly never heard of that), but that's what Doom is here for (he has a counter to that...ironically for Magneto).
Also Magneto likely has far better EM control than Ultron since it's allowed him to do nearly impossible things and defeat very high tier or herald level opponents.