To begin; I welcome different views. This subject is difficult because I'm outlining a way to judge. That is uncomfortable sometimes. Also, I have worked with very good coders who didn't meet my guidelines.
While I was the President of the New Zealand Open Source Society I have also been a professional developer for all my professional career. Open Source attracts people who care about the technology, and so those who have contributed to open source projects have demonstrable skills. Further, because it is open you can review it. This means you can objectively evaluate skills. This isn't possible with private commercial projects.
I'm not saying people who pick up programming in University are poor coders, rather that this is not a positive indicator for passion.
In response to your question about developers coming in and wanting to change the stack, I actually I welcome such challenges. To me the team is equal, and if you can't justify a something perhaps you should re-evaluate. New developers are not invested in the project so they have fresh eyes. Furthermore I want people who are willing to question and challenge rather than muddle through with whatever they are told. I'm missing out detail here; obviously we don't rewrite systems just to please the new guy.
The one thing I have not discussed in this article is that good teams are more strongly correlated to success than amazing developers. Building a team might start with choosing the right people, but without a commitment to giving them the right environment it is pointless.
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