You assume a reasonably competent group. Thats an error. In LFG you'll have to contend with the bottom feeders of the bottom feeders of WoW.
You can't expect to have a healer well geared enough to ignore the debuff
You can't expect to have a group well geared and on point enough with interrupts to aoe the adds on moroes
You can't expect LFG people to be competent in the sense of the word.