Honestly Nog showed he could beat Mir . The first fight started all those memes about Nog being an excuse machine out of the hospital. It was so weird to see. Every once in a while Mir would strike with people and his hands were glued to Antonio's chin. The second time Nog rocked him and gave him a kimura
But if we were to humor our imagination and speculate timeliness. I think either could beat Lesnar. Finish him too
This hypothetical of Lesnar-Nog is interesting.
Do you reckon Nog could tap Lesnar? I'm not totally convinced. I'd favour guys like Mir and Fedor to tap Brock (obviously Mir actually did) - less sure about Nog, who is more likely to apply a chokehold/throw something up from the bottom.
I think to tap Lesnar you'd really need a brute force/deadweight-type submission effort - a limb, something you can threaten to snap.
I'm not at all convinced Nog would choke him out, and I'm not convinced he completes any kind of armbar/kimura in the same manner as a Mir or Fedor, either.
Beyond that, Nog's best chance is a Decision - but only Heath Herring went the distance with Lesnar, and he lost badly.
I think it would have been a great fight, but honestly? Lesnar might have won that.
Just some rambling ass thoughts on the matter. I just don't think there are many smaller/finesse heavyweights that would have beaten Brock. You either hit him hard as fuck, shut down his wrestling game, or you threaten to break his limbs. I don't think there are many other options.