Again, with an assumption that 16 is the minimum. Which it is not. Its 15.
That is the baseline, upon which racial modifiers are then applied.
T)he game does not say Dwarves cannot be Bards, or that Tieflings cannot be fighters. 'Supposed' to be, is mnot a thing.
There are Attributes, Races, and Classes. The game was designed with archetypes in mind, but unlike prior editions, you are not explicitly forced to adhere to any combination Wizards deems acceptable. Feel free to roll that Orc wizard with the -2 Int, the game allows for it as it was designed to allow for it.