Mongal? She's more like Stompa than Darkseid. Oddly enough its apparently canon that she's less powerful than her brother. Probably not MUCH less powerful, maybe it's the old "faster but not physically a strong" thing?
I'd LOVE to see Mongul or Mongal make an evil super-team to annoy the League! Legion of whatever stories always make a great way to create a threat that you NEED the JLA to deal with because 1 on X fights with supervillains usually go badly.