I would argue this is naive and there's very little evidence to support this opinion other than just wishing it was true.

It may happen on smaller projects with few users but not in meaningful large projects.

> there's very little evidence to support this opinion other than just wishing it was true

Building a brand doesn’t require submitting to someone else’s open source project. You can do the same thing by creating your own OSS project.

For a lot of them it’s probably a little of column A and a little of column B.

If people are submitting in their real name it’s more likely they’re building a brand. I also think it’s possible for someone to genuinely think they are helping without trying to build reputation.