I guess that a really experienced developer would finish such simulator in like half of the time. afaik, US is Dan's first big project so yea. I've got no problem with that btw.
I would say we each have rather a lot of experience.
To elaborate; what makes this project somewhat hard is that it is not a simulation and it is not a game.
Some of us are quite experienced at game development and could probably have made an ordinary game a lot faster.
Some of us, myself included, are from a more scientific background and could make a simulation a lot faster.
I cannot count the times I have pulled hairs out of my head (which is hard when you cut it down to 1mm in length) in frustration over not being able to just do things scientifically correct, and let it run for a long as it takes.
...so... it may look like we are running around, constantly messing things up, but it is really just to try to constantly change and optimize things, so it is faster and prettier and more correct than it was previously.
This alpha phase is when we have the liberty to really try things out, and tear stuff down again, when we come up with a better solution. Later in the process, we cannot really make that drastic changes.