You can't port the whole raid, the portal can only be used 5 times before it has to recharge, gaining 1 charge per 15 seconds. Also the range is 70 yards max.
If you put one portal at the edge and make people stand slightly off-center they will always be carried in the same direction and could click the portal as they fall.
You CAN port the whole raid. He was talking about class stacking. If you have 5 warlocks: 5*5=25. The problem isn't necessarily that you COULD port the whole raid, it's that it would require 5 Warlocks to do so. If this ever became required to down a boss, it completely goes against the "bring the player, not the class" philosophy.