i wonder with all the work Neo ordered them to do to Sting (Erasing both Auel and Stellar) that he lost some of his skills. As irrational as it is thats one explanation as to why Sting sucked.
Another explanation (one i reckon is correct) could be that the orb pilots are actually really good, i think if you stuck them in say Strike or Aegis they would be on par with Mwuu or Lunamaria in there respective suits. The difference is that there MS isnt supposedly as good so there a bit like Athrun,Yzak and Dearka in Yaku's.
Sting clearly should have had his unit spilt up and shoot down the multiple Orb suits only to be killed by cagalli in her strike after seing her pilots get vaped (that would have been great to see her kill somebody)