That's a problem with the way the game is, not the content.
In most MMO's you pick one class and you stick with it, or you make a new character and level a new class, so in those situations you either go on your main class or you switch to a alt character.
In FF11 people used to throw BLM's and SMN's at bosses all the time, FF14 is worse because you can change whenever.
I am huge fan of being able to change job between battles but I can't see them fixing this issue with stacking classes/jobs any time soon if ever, because players will always abuse the easiest strategy.
Like I said in a previous thread the only way to do this is if people stack too many of one class to remove "strength in numbers" or something.
Normally I'm not really in favour of penalising players, but I think its the only way you will get people to stop class stacking... even then they may still do it if the advantage of class stacking out weights the loss of the buff.
