Player run events for low and mid level nf tournaments. Group your opponents by class and rank. Within ten ranks for example. Overall rank this is. That's what I would do.

Balance weapons so that store bought are powerful enough to provide a chance of fighting against rares and punish the hell out of ganking tonnes of levels below you but reward for killing someone around your level or higher. When I say higher I mean within a level range if your own. I don't wanna see 0/2 putting a cap in the ass of a 60 runner just cos he is a clan mate. The problem of sympathy mules of old would need to be carefully managed to stop exploits too. However all of these suggestions would need to be heavily tested to remove any kind of exploitable actions.