Welp, even though I only list 2 teams in my sig I have 10 lvl 70's from my pre MBing days that I have messed around with in level 70 instances and a few easier heroics with less than ideal group make-ups. Even with less than ideal group make-ups and a majority of those 70's having very bad gear I've still killed a few heroic bosses. The biggest hang-ups I'm having isn't the group make up but rather they gear they are currently in. Given enough time I'm sure I could make them work fairly sucessfully. Sure I wouldn't be able to kill and clear every heroic with lightning speed while having ez-mode turned on but it is doable.

However if you want to be able to kill the most amount of heroic bosses there are a few abilites that would be highly recommended to have in your group and Fear control imo is one of them.