The Defense Paragon.

If Salvos and Salvin were allowed to go all out in killing the normal Vipers, then they would have created more paragons that they can't fight. Soverick would be the one to deal with more paragons on his hands. So rather than take on more problems, Soverick sent them here where their damage output will be put to better use. 

Ghaster accompanied them to provide quick help or response since he is faster than the two of them. But he is not happy about it. Salvin on the other is quite happy about the arrangement. Soverick claimed that they will have their use here so he is eager to let loose.