Yep they are complicated but the biggest problem by far to a sole developer is we become a Jack of all trades and a master of none.
Modeller, texture artist, sound engineer, aerodynamicist, systems analyst, computer programmer, tea boy and general dogs body. Thermodynamicist
And that's why we should try to form teams to develop things. I know it's difficult, but in a sense it helps too to compensate for the extra effort and process. And also I think it's more fun too.
I know I can do a few of these, but not all of them, that is what is keeping me from developping some aircrafts.
On the Apollo 50 we worked as a team and it seems pretty much each one has a specialty and we collaborated very well. I don't think anyone in the team knew how to do everything well, except maybe Tom.
What it also says is that anyone that does it as a single developper earns tremendous respect, because it's so complicated and it would be so easy to stumble on one process and not been able to master it. So kudos!