Might I suggest that maybe having imposter syndrome is not such a bad thing. You could interpret it as being keenly aware of gaps in your understanding. It's also much better to admit when you don't know something than to act as if you do.

It's also important to recognize that just because you're competent in one aspect of software engineering, doesn't mean that you would be in another. That being said, maybe you're weighing technical skills too highly. By now you must've realized that technical chops are only one variable in the equation that makes a good software engineer. Other things such as communicating through writing and speaking, understanding the needs of the business, being able to get different teams in an organization to work together are important. One could even argue that they're more important as you get promoted and move up the career ladder and are tasked with more leadership tasks.