I think Kris Allen's underperformance could not be attributed to simply being 'inferior' to Adam Lambert...Adam sings music that are more 'current' (mindless bubblegum electro-dance catchy pop, and he even looks like a female and could sound as high as a female does, so...) and he is definitely more aggressive and with more promotions. And if you count "Time For Miracles", Adam actually had 4 singles with "For Your Entertainment", "Whataya Want From Me" and "If I Had You". Kris did not include "No Boundaries" is his debut so he's only gotten "Live Like We're Dying", "The Truth" (featuring Train) and "Alright With Me" so far. Kris' underperformance also due to horrible single choices. Granted, LLWD was a hit, but it was stupid to release a cover by a band that was not really known in America (and it was only their b-side) for an American Idol winner. Not to mention the track shows no vocal ability whatsoever. Then, "The Truth" which could be the bomb of his career.
It is also hard when you have Adam getting all the priority in promotions (that infamous AMA debut performance for example, mentoring on Idol etc etc) and the media circus constantly surrounding Adam. Kris had to live with the perception that he was "not good enough", "shouldn't have won", "the other guy" etc. On top of that, Jive (Kris's label) is famous for being stingy on promotions as well.
LLWD being a "cover" is actually never a problem. Hardly anyone in the US even heard of that song until some fans dug it out. TBH, the only people who saw it as a problem were people in the Idol bubble. Outside of it, casual listeners didn't care, critics didn't care..... and it's proven when it becomes a Top 10 Pop hit. Whataya Want From Me is a note-for-note "cover" as well, and again, because it's a good song and being sung well, no one cared.
Speaking of covers..... I didn't know Beyonce's "Smash Into You" was a cover of Jon Mclaughlin's "Smack Into You". LOL, changing one word, how creative
...... Sorry, I digressed