If you ask me, any Mac computer made in the last 5 years far exceeds what’s necessary for graphic design. To build on sprout’s comment, you can never have too much screen space.
3D modeling is a different story. The actual 3D modeling process doesn’t take much processing power. But you can never have too much processing power when it comes to 3D rendering, especially if the models are animated. That’s why movie studios use render farms.