The mass infighting serves a very good pupose, as long one's minions are busy fighting among themselves then they're too busy to join up to challenge you. Also, the fighting keeps your minions sharp, the weak or stupid die and are replaced by new minions, who either keep up or join their predecessor in the corpse pile. All of which works to the advantage of a Sith Emperor.
The mass infighting is destroying the Sith from the inside. Lesser Sith team up to destroy more powerful Sith, who in turn is defeated by even lesser Sith. This is a downward spiral that would destroy the sith, and it will. This is the reason the Rule of Two was so successful. Only the stronger could win, there were no allys to help.
Think of this:
Revan was dark lord. Malak destroyed him and declared himself more powerful. Malak rises, revan falls. The lesser takes control from the powerful.
Satele shan once said, "a united sith is a force that cannot be stopped."
But you see, they arent united they backstab, and it is the reason they fall, like all animals must.