AFT05MP075 ADS model has been optimized to match measured RF performance.
DC parameter was not specially tuned. In fact, most of the difference between datasheet Figure 3 and simulation is determined by different gate threshold voltages of the model and of the datasheet instance. This value is about 0.5V more in the model vs datasheet sample.
Note 1. Gate threshold voltage can differ from sample to sample due to production spread. Datasheet specifies VGS(th)=[1.7,2.5]V. Figure 3 was measured on the device with VGS(th)~2V whereas the threshold in the model is closer to 2.5V.
Note 2. The accuracy of DC model is not critical, since the gate bias voltage of each device has to be tuned individually.