1. It is more great to do something with a greater handicap.
2. Not existing is the greatest possible handicap.
3. The greatest possible being is thus one who could create the universe despite not existing.
I think OP here is meaning "great" in some intellectual capacity, that you are just as powerful or great if you can make up your lack of greatness in one area with another form of greatness, something I don't see as greater but equally great. Is it greater to be successful by bootstrapping off the success of your forebearer or greater to be as successful when starting from nothing? It's a classical argument but to me it stands on just as rational ground as Gödel's argument.
I would argue that impossiblity, rather than non-existence is the greatest handicap.