Have fought many groups that do just that (part will peel off veil/ hide for a portal bomb or just try to flank the group), have done it with my guild as well (when playing off another larger tag we would try to bait the zerg so our other tag could hit them when they were on cd or flank while they go for the other tag). Think once a tag hits a certain size without a second tag they turn into the back and forth blob fights that are more attrition based to win.