I believe we were told this one in this series proper: L > Near, and L > Mello, but L < Near + Mello.
Or, in other words, they could beat if they managed to work together.
^That's Near's opinion, so it's not exactly what one might call unbiased.
Stick of the Fallen
Had Cool Shibitaku gotten his hands on the Death Note, he would have defeated Light and L without ever losing his anonymity.
"Oh great! Let's pile up all the useless cats and hope a tree falls on them!"
Splendid Ninja
I think Near+Mello would at least put up a really, really good fight against L. Near doesn't have the initiative and Mello doesn't have the patience, but together they balance each other out pretty well. And I think Mello could give them an edge, because he acts more on emotion than he does on thought. Even if he was decidedly working with Near, I think he'd retain a certain amount of unpredictability.
"With hard work and dedication, I will become a splendid ninja!"
L would easily crush them.
they only got light after he no longer had rem as his kill-all (he should've had her do in L before getting misa setup, there was no point in getting rid of rem.) if light didn't have the misa-rem combo, then he'd have no chance of finding L's name.
mello was too short-tempered, near was too aspergery