I agree that if the prioritization decision was made as a trade-off then this could be a question of design, but something would need to be said about that. Saying "I like the design of my car because it goes fast" doesn't really make sense unless you bring up what was changed (e.g., the aerodynamics, or the missing backseats, or whatever).
Speed is part of the user experience, and good user experience is the goal of, and usually relies on, good design. But the result -- speed -- is not itself design. Otherwise there would be no distinction between good products and good design.
