Indeed, functionality is higher in the sense user has more options in how to connect the amp to a DAC, be it built in or external.
But my understanding is that at the time of developing their GaN amp Peachtree was solving for how to make that level of amp performance available at a lower price point. And they realized they could do without the analog to digital conversion needed inside the GaN amp. It follows their approach should deliver a given sound quality at a lower price point vs competitors with analog inputs, at the cost of flexibility in inputs. It remains to be seen how GAN 1 compares to other amps in the same price point, though. But I can see use for such an amp and find the concept appealing