Mostly due to relative comparisons to others- Mon-El at his best is generally Superman's near-equal (and modern Mon-el is not Superman's equal), and in recent times Black Adam has been generally performing on a level where it takes more than a single top-tier to match him.
We should confirm if that's a pre or post crisis feat..
From the art, it looks post crisis, but I'm not really an expert on post crisis LOSH, and while I'm much better at pre crisis I haven't seen every single issue..
It's Post crisis. And from feats, Mon has this. Even TT admitted he's the strongest of the Legion. Not superman. But it's been that way, pre-crisis too.
Mon-el's body can take magic attacks. Hell, I believe he took a blast from Mordru pretty well in a run of Legion. Magic won't be an automatic win here. Especially if we use the version that tore up a weakened TT.
Have you seen Mon's respect thread? He's moved a white star from one solar system to another, withstood the heat of the sun, crossed time barriers, and killed the Time Trapper, who was weakened. The same TT who said Mon was the strongest of legionaires. Respect.
What's the point of making this thread if you're just going to argue against anyone who debates the side you don't agree with? That's pretty much bating.
Mon EL is stronger at his best than any of DC's other Herald levels in space feats. He just isn't cnsistant. Sometimes he's a feeb.BA can't really win tho. Monel kills BA in speed and strength. Split die to Monel's softer nature.