One of the big shortcomings of Contagion is that it was only ever a significant gain when combined with buffs like Raging Strikes and such. The next two times you used it, it would be an extremely tiny gain.

Now with Dreadwyrm Trance and Tri-disaster, you could get some more mileage by extending buffed DoTs every minute instead of just once every 3 minutes. This could close the gap between the pets, depending on the encounter. I haven't done any testing, though; I'll worry about it after I get my Ravana book.