Really depends on the domain. I've been in jobs where the domain was much harder than my job as a software engineer, but I've also been in jobs where I quickly got to understand the domain better than the domain experts, or at least parts of it. I believe this is not because I'm smart (I'm not), but because software engineering requires precise requirements, which requires unrelenting questioning and attention to details.

The ability to acquire domain knowledge quickly however, isn't exactly the same as the ability to develop complex software.