By "adding" do you mean to really add strips to their skills and keep AD as well to destroy equipment? Or do you want to replace AD for the strip skills? Because if you replace it, it will be alot easier for the usual partys since I rarely see people tank the monsters and give the chance to get stripped by standing close to them. So if you plan to add strip skills then i would suggest to keep the AD skill as well. =)
and sure big parties dont tank much, but it affects the smaller parties and could still be relevant to big parties with a high enough occurrence and/or success rate.
If it does push people to make bigger parties all the time then it has successfully done its job by making muspel more of a party dungeon rather than a duo-doable-dungeon.