I would argue that those skills are indeed the most important part and are really implied base requirements for any job, as without them, it's difficult, if not impossible, to effectively work in a team.
And the mindset which doesn't assume that one has to be able to work in a team to be a good developer is why we have "rock star developers".
I would have agreed with Allen a few years ago, but lately I'm really thinking that they're even more important than, say, 50% of your skills and efforts. So, I'd say core. Like 70%+ :)
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