While simplicity is used to define minimalism, it’s anything but simple to create a good minimalist design. To master minimalist design means to master design. It’s harder to pull off because you can’t hide behind ornament and decoration.
All minimalist designs should not and do not look alike. Minimalism does not mean take everything away until only black text on a white background remains. It means communicating as much as possible with as few elements as possible.
It strikes me that instead of a design being minimalist or not minimalist, it’s more a case of to what degree does the design embrace minimalism. We can strive toward it, but even the most minimalist design could be reduced further.
None of this should be taken to mean that every design should end up being minimalist. Different design styles set different moods and invoke different emotions in your audience.
Minimalism is reducing your work to the essential and using less to do more. In order to do minimalism well you need a strong understanding of basic design principles. When you master minimalism you master design.