I believe you need both. My other question is, which method do I start? It depends on your time and resources. You need a list to do email marketing, to make it work, you need to establish your audience and subscribers, if you're into it, then it will be best to start paying for traffic to build a list to save your time. On the other hand, your contents will drive you traffic, investing time and effort to produce quality content will get you a position, all the way to being looked up as an expert, perhaps.
Content marketing, as far as I know needs a little bit of SEO support, you want to attract organic traffic to your creations, but the advantage here is, it drives you consistent traffic for months or even years to come, while in email marketing, you need to produce and increase that list every single day to make it work, But again, it saves you time in creating contents, you just send that email and tweak a little bit to increase your open and click rates. Hope this helps :icon_rock: