Thanks for the response! To be sure, those traits are important for a developer. Arguably more important, because if you can’t work well with others you won’t have a job for long.
The Project Euler problems aren’t the only thing a developer should practice — I hope the article doesn’t come off that way!
The problems are a great way to sharpen the saw to improve your skills on your own. Use them to become a developer who can understand a problem, intuit a suitably optimized solution, and quickly implement vanilla code to solve that problem.
Of course, Project Euler isn’t the end-all of learning experiences. And of course solving them only benefits you. You’re entirely right that working on a team to solve real client problems would be ideal. And a developer’s personal portfolio should definitely include useful projects that deliver value.