I think you are over estimating the number of contributors an average open source project gets. Almost none of the projects go to an extend to deliberately avoid new contributors. Its really hard to get people to contribute code to most open source projects. A good maintainer is incentivized to make it easier for new contributors to contribute. Not the other way around.
Well, I'm afraid whatever the system might be, it's definitely not going to favor the newcomers.
(edit: formatting)