I'm sorry but I am not completely sure what you mean in your comment. Every party wants to have the most Offensive and defensive abilities possible. If the world can throw heavy enemies, light enemies, or swarms of enemies (there are more variations that could be used but these are the ones that come to mind) at you then the only way to ensure that you are keeping yourself secure and doing the most damage possible is to 1: study the area where you are going, and the monsters you will encounter, and 2: ensure you equip your party with the best men/women for the job.

If you are headed into an area where you will encounter a lot of light armor units, you would be better off for bringing more pugilists, but to leave without a marauder would be foolish as you would have a major hole in your offensive abilities against any armored enemies. The fact is that these classes become irreplaceable because they have something to offer that fills a hole in the weakness of the other classes.

So if you see a hole in my plan you are going to have to be more specific as to what it is because, honestly, I am kinda confused as to what you are trying to say is the right course of action, and why my idea fails.