The reason why I would not call MK a 'premier' designer is that it seems to copy or have very similar designs to other premier designers, for example,
Prada's double zip tote (MK Sutton Satchel), Louis Vuitton's Totally tote (MK Jet Set Top Zip Tote), Louis Vuitton's Artsy (MK Skorpios).
To me, a premier designer would have a signature design that is distinctive and unique e.g. Celine, Hermes, Givenchy, Chanel, Balenciaga. When someone says Celine, you instantly think of the Celine luggage. Hermes - Birkin bag. Givenchy - Antigona. Chanel - classic flap etc.