That's not a committer, that's someone who submitted a patch that got committed. A committer is the one who actually applies the patch and can push the branch into the mainline repo. Committers decide if something is worthy of being merged.
Now that aside, yes this plus reviewing patches to get a wider feel for the codebase is how you eventually become a committer.
Best way to eat an elephant is one bite at at time.
There was sort of a fuzzy "major" contributors (https://www.postgresql.org/community/contributors/) which were people that contributed major features and then a list of other contributors. Depending on who you talk to this is either dated or a pretty close attempt at reflection of reality but not perfect. In recent years they expanded the contributors to include others that were contributing in non-code ways though it's still a decent place to find people contributing to major feature sets.
Of course this is not to be confused with the core team–which is more like a steering committee. But not so much steering committee of code and feature sets.