Take a look at linux, firefox or chrome code and tell me if you understand. That's a hell of a scale, if you are capable of doing better, you are the best programmer in the world. I think you are suffering from the Dunning-Kruger effect.
I'm not quite sure you understood the question. I didn't say I was capable of building Firefox, I said that what I have been paid to build has never been complex. I'm wondering if that's common. People building Firefox or Linux isn't the typical programming job.