You don't want to have limitation of what you can do, Let me ask you this. What if all all SM are taken for dredge and you don't have a choice to form the group? that just pointless in my opinion. If you think those forms of groups are OP then why don't you form one your self if it's OP? so does it make sense? lol
what if my friends are all Assassin and want to play with them in dredge?
having another Character is not fun and I personally don't have a lot of time to play/create another character?