I try to take a more statistical view of it. I mean, if it weren’t okay to be average, there wouldn’t be such a thing as an average in the first place. It’s by definition weird to not be average. And we all know that most people aren’t weird.
I like your idea of measuring yourself by significance, though, because that’s a much more meaningful metric and one that’s much more in our control. Being of service to others makes us significant no matter how average we may be otherwise.