I see a lot of posts about this so I think i'm going to step in. First of all I would like to note that the primary factor that leads to class stacking is the community taking the easiest way out always, and class stacking is easier to realize the potential since it's a simple strategy, whereas stuff that involves multiple classes might even be more efficient but requires more planning and better execution. But I digress, that is not my point in this post.

My point is thus, for people who want SE to do something against class stacking:
Quote Originally Posted by Rukkirii View Post
We wanted to give everyone an update on battle regimens; once we have finalized the battle fixes and implemented jobs in patch 1.21, we will move forward with our plans to re-implement an optimized battle regimen system to go along with the battle system. Since combos have just recently been added, we will also be looking into the possibility of changing the battle regimen system.

Due to this, we are unable to provide any additional information or an implementation date, but we will be sure to let you know of any other information that comes our way.
It's old, from January. They are, in fact, going to implement a, theoretically, less stupid Battle Regimen, system. Essentially, for those of you who joined the game after they were gone (like me), a multiple-character combo system, and if they build upon the basis of the existent Combo system, it will probably involve actions from different classes. Hopefully that should alleviate the 'problem' of class stacking.