All rounded party - help me out

[Melusina]

To me, all rounded party doesn't necessary mean different roles, e.g. archer/caster/tank/healer, but also different classes/multiclasses with as little as possible overlap... but, for unknown reason, I have hard time with that as we are restricted with only five party members - if one of them is dead weight it pulls party more heavily than in six-person party.

 

Do you have some advice how to build up good party?