Mercule
Adventurer
Agreed. The way 5E backgrounds, proficiencies, and tools work, an all-wizard group could still be quite diverse.As for duplicate classes, I wouldn't mind playing a campaign with all characters being the same class. A party entirely comprised of wizards could make for some interesting roleplaying and adventures. So I wouldn't have a problem with two players of the same class either.
Heck, an all-fighter group would still be able to have some level of magical support, even.