Comic book Magneto is a bloody powerhouse of a monster to be sure.
He can shield himself with an electromagnetic barrier sphere, blast foes with pure electromagnetic force, and pretty much manipulate any kind of metal he wants (even the Earth's magnetic field which he once used to cause a planet wide EMP shorting out all electricity and killing hundreds of thousands).
I'm not saying the Avengers can't take him but they wouldn't all come out in one piece that's for sure. The Avengers confrontation with Thanos left Captain America, Black Widow, and Iron Man either dead or out of action so I can only imagine what price our heroes would pay taking on one of the world's most powerful mutants.
I'm actually hoping they introduce Mutants and eventually put them in conflict with the Counsel of Humanity (led by Bastion). Hell, maybe they can even do the Onslaught arc right in the MCU (which unfortunately they couldn't in the comics but the movies could be different).
I definately want to see Hellfire Club Emma Frost strutting her stuff down Times Square while dressed in lingerie and draped with a large, long, and fluffy white feather boa. She's one of the few female heroines/villains confident enough in her sexuality to use it against men and not have it bother her. 😉 😀