That designers sometimes prioritize gameplay to the detriment of the experience is a matter of confusion. On one hand, designers are craftsman, creating gameplay. On the other, designers are shepherds, guiding elements from all disciplines into a powerful sum experience. Because "design" means both things, some designers assume that crafting, like shepherding, should direct other disciplines.
But people play games for experiences, not mechanics. Crafting design is not necessarily more important than crafting audio, art, or story, and its true value can only be assessed in reference to the experience it informs.
Design should be "experience first," not "mechanics first." It helps guide designers as shepherds and advances their craft, inspiring innovation because so many experiences await exploration, and because even familiar experiences treat gameplay as a variable to be filled in interesting new ways, instead of the end itself.