>> Major features were added over the course of weeks! >> — to say nothing of getting the overall architecture right from the start.

[Most likely] it is not that they got it right, right from the start. These 'awesome' programmers would have spent weeks before getting it right. These classify as throw away experiments and they keep at it till it satisfies their own internal target of what the solution should be like till it is right.

The best parameter of that right could be say the simplicity of the overall internal implementation and the exposed external API.

Now I am not saying that there are not geniuses around, but even if they are getting it right, it will still be backed by countless hours of hard work and practice.

Most likely asking these awesome programmers how they are getting it right, will throw some more light.