I dont believe mercenaries are suppose to add to origin characters ... they are suppose to replace them.
Party of 6 could be usefull in many ways ...
But mercenaries are not good argument for it, as far as i know, if you would have party of 6 ... there is litteraly nothing forbiding you to make 6 custom characters, instead of 4 ... And (speaking about single player, obviously) you are just where you are now. :-/
In the end there is nothing disrespectful, or insulting about mentioning that some thing is obvious ... if you find such statement as personal attack, i believe you have problem. :-/
I still dont understand why cant we change Race for our hirelings. Lets us play Githyanki as racist as they trully are!