There are differences between classes and the roles that you can have in a party. In 5e the different classes are very flexible, many classes could fulfill different roles. So usually it´s not needed to have 6 different characters to take care of 6 different roles in the party.
Already gave you lots of examples, if you don´t buy it and think I do not describe it accurately I hope you have any facts that back your claims because yours sounds a baseless and prejudiced opinion from my viewpoint.