Headcanon: Alternate Michael is a Cannibal
So I have a theory as to why Alternate Michael was so much more powerful than our main universe Archangels.
Notice how the battle between Alt Michael and Alt Lucifer tore their world apart, and yet Alt Michael casual toyed with Main Lucifer?
Notice how Alt Michael immediately recognized Main Lucifer as Lucifer, but Main Lucifer didn't know Alt Michael was Michael until he was led to that conclusion, and even then called him a knockoff?
I think Alt Michael didn't simply kill Alt Lucifer, but after besting him, absorbed his grace in order to further power himself up. Why? Well remember, Alt Michael had a beef with God and wanted to kill him, but he knew he wasn't strong enough to do so with just his own might, but maybe if he amped himself up? Eating Alt Lucifer's grace would certainly give him a boost. But I don't think he stopped there.
Notice how Alt Raphael is nowhere to be seen? Well, I suspect Alt Michael killed him and ate his grace too, seeing him as no longer useful as the war was now over. After all, Alt Raphael was a useful general when Alt Michael had hordes of demons, possibly including Apocalypse World's Princes of Hell and Knights of Hell, to deal with. But with the enemy gone, Alt Raphael would no longer be a useful soldier, but instead a potential rival for power, since he's one of the few beings left in that universe who could even REMOTELY challenge him. So he'd want him dead either way, why not consume his grace too, so he could get even more powerful when he eventually caught up with his old man?
It's also possible he hunted down Alt Gabriel and did the same to him, but based on how genuinely surprised he was to see Main Gabriel, I suspect he was never able to locate his universe's version of his baby brother to snack on.
This theory explains why he's so much stronger, why he was hard for Lucifer to recognize, and why he'd be so sure he could handle his old man, God. God and four Archangels was enough to handle Amara, so maybe one Archangel, fueled by the grace of two more, would be enough to challenge God. That's what I believe Alt Michael thought anyhow.
What are your thoughts?