The problem is: It forces you to take fire and earth, because fire alone does not do that much either. Only the interaction with both does the real deal, as you say so.
If don't have that knowledge and just start the way you expected to play, you could easily feel screwed. Same goes to the fact, that the early stage is pretty hard, if you don't know what you have to do, to get your exp. Also in the early stage of the game it is much harder to be that versatile with all those different kind of skill for every situation.
In DOS1 water and air were good to lay a huge field of decent CC, in DOS2 the combination is pretty useless. You don't have to worry to get stunned, as long you have enough shield left.
