Find its interesting that people are looking at increasing the difficulty, but wont even consider power creep on each individual archytype. Take the damage potential of blaster and compare it to a defender, both with full sets and incarnates.
Im not suggesting the a defender should match a blaster, but with the games use of % based increments that gap only got bigger and bigger, this can also be applied to any ability/sets ingame. (includes my PB Dwarf and perma LF)
Atm, the way the game makes it harder is to simply increase the mobs level and to increase their numbers which to me isnt a good way to make it harder, but instead youl end up with what is called bullet sponges, and in certain groups, your team might face much of a threat, but might take even longer to complete missions or AVs simply cannot be taken down due to their resistances and health regen.
There are simply way to many power combos to effectively find a solution for game difficulty, do we cater for the strongest players and sets or do we cater for weakest? If the game is too hard its impossible, but to easy its not challenging. But at least not challenging doesnt provide content barrier.