How I think they should implement the dual classes is say for Marauder, with the great axe they have the weaponskills and abilities they have now but for their second weapon which could be dual wielding 2 axes they have all new weaponskills and abilities. Now they cant pick the great axe skills if they are dual wielding the axes, and for picking abilities and weaponskills from other classes you pick which set you want. An example would be with gladiator is sword and shield or greatsword. You would only be able to either or set of skill and not from both. Now as a marauder/warrior as a tank you would want the sword and shield version but as a DD you would pick the greatsword.

This would also give a bit of a difference between a marauder/warrior from one another. You could have one with more of a tank role and have another focusing more on DDing.