You overestimate the difficulty. The real difficulty is not the individual unit, but the mass production.

Many small startups have produced low volume of cars that are competitive.

The truck itself is really not that magically complex as you assume. And Tesla has lots of experience with the most important parts like batteries and motors. Far more then Ford.

What people here underestimate is actually the supply chain, specially of batteries while overestimating how difficult it is to make any individual truck.