Shield are a well coordinated unit. They've taken out John Cena, Ryback, Team Hell No, Big Show, etc.
They would have no issue with Sting or Hogans old ass.
Aces and 8 have not been booked as a legitimate threat. And 2 the story is retarded. Hogan is the GM/Comissioner of TNA, which has a pretty large roster. All he has to do is order all of his employees to bum rush Aces and 8 and it would be over.
Shield are targeting certain individuals who represent injustices. It's not an invasion. They get in, complete the mission and exit like a special op team would do.