Three: The tires have a smaller contact patch.
Before you think of what happened with the FR-S and BRZ, stop. Yes, the Subaru BRZ and FR-S run narrow wheels and tires, and have a square setup so that all wheels and tires are interchangeable. Porsche went a different route. While the Porsche 911R also runs smaller wheels, the setup is staggered. There are extremely high limits of grip available, especially when Michelin Sport Cup 2 tires are the primary source of grip. Why opt for a smaller contact patch? It makes a car more nimble. The suspension comes straight from the GT3. Pitch and yaw responses are more immediate. Changes in weight balance are more pronounced. That is a crucial part of a purist driver’s experience.