But come on... Why would Mello be named that if he's just about anything but mellow? Near comments on the fact that Mello's shortcoming of becoming L is that he has too much emotional baggage. Mello is pretty angry. Near is the mellow one.
Well, why would Near be Near? He is quite far from humanity and the outside world, isn't he? He is far from able to accomplish anything without the help of others, or even take care of himself, for that matter.
Mello is loud, impulsive, and aggressive, so I do see your point there. I think that they both chose those aliases that contradicted them on purpose.
I actually think that Mello's emotions make him can go both ways. On one side, he is very well-spoken, intelligent, and insightful, but his inferiority complex leads him to do reckless, selfish, and infantile things, as well as loose sight of what is truly important, and even end up killing others (sadly). In the end, he did know what was the right thing to to, though.