Let's not get too stove-piped here.
Of coure, pilots can navigate an aircraft. Otherwise, how will single seat cope! The advantage of having a 2 seat ac is the workload that can be taken on by the crew.
The argument is often whether 2 seat is better than 1 seat. It depends on the ac, the avionics, the task and, what is often forgotten the task that the ac was never designed to fulfill!