i always took that line nas said as a diss to eminem...just think about it...if nas really respected eminems level of rhyming why did he say "eminem got you on renegade"...thats equivalent to saying to someone who lost to a retard "even (insert retard name) beat you on a 1 on 1 game...if eminem is so superior then its common for him to get jayz and any other rapper on they own shyt...but it just seemed like nas was laughing at him like "how you going to let the white boy get you on your own shyt"...this is my 2 pennies...
Eh. I've never thought about it that way, but your perspective does make some sense.
But I always interpreted as just being like - it's your album and your song, and your guest artist outshines you, you must not be as good as you claim. How can you be the best when you're not even the best dude on your own album. It just makes you look bad to get outdone on your own shyt.
Only example that comes to mind is if you had some main/headline/big actor in a movie as the main role, yet some secondary/supporting actor clearly has the better performance, it makes the main actor look that much worse. I suppose if they both straight up sucked, you could say "man you must really suck to get outdone by that scrub," but then you wouldn't say either performance was any good (like Nas sayin Eminem murdered it). It just makes it look like the main actor isn't as good as they seem when posted up next to better talent.