That's a false dichotomy. I have been a contractor for most software engineering jobs I have done for many years and all of them were very complex. None of them

That's a false dichotomy. I have been a contractor for most software engineering jobs I have done for many years and all of them were very complex. None of them were for a particularly high rate like $300/hour. The rate actually has generally been fairly unrelated to the complexity. Possibly the biggest determining factor in my rate has been how much savings I had (usually close to zero) when I needed to find another contract. That determined how selective I could be and how long I could spend looking. If your option is to take the next contract or miss rent, you take what you can get, often for a discounted rate.