I might be wrong here but I thought that a Debuff can only be apply once per caster.
IE the sg from earlier post. no matter how many times "Blaster A" tosses his nade it only debufs it X amount. Not X time number of nades
Were as "Blaster A" and "Blaster B" each toss a nade then you have X plus X
This stops a "Blaster A" from Debuffing a Arcvillan down to what ever the Minimum To hit chase(5% Or somethis I herd)
Replace Blaster with Your archetype of choice and Nade with debuff of choice. Your mailage may varie