Content is definitely something on which you should focus first, as you won't even be able to get relevant backlinks if your content is poor and it doesn't provide a good user experience. Once you have your content in order, you can proceed with working on backlinks and connecting with reliable sources, so the answer is pretty obvious here.
I agree. There is no such thing that one thing is super important, and the rest can not be used. It's always a matter of balance.