'"The frequent refrain that open source is a pure meritocracy must be reexamined."'
That's always been false.
I'm pretty sure it's a misrepresentation of the original argument. Making something open source obviously won't magically make it meritorious. However, making something open source can be a huge step towards becoming truly meritorious.
The very fact that this study could be done and this bias exposed is because the projects studied are open source. We don't have similar studies for Microsoft, Oracle, IBM, etc because the source is closed and the commit history even more so.
Open source isn't perfect and no ibe should claim it is, but it's a more transparent system than the alternatives. And that's a good thing.