The controversial answer is ... content marketing might not be right for every business model. Some businesses with a high LTV (lifetime value) client might kill for 1.8 sales per month, whereas those in the "widgets", stack high, sell low, business would struggle to make ends meet.

That said, and assuming yours is a business where the LTV is considerable, there's more work that can be done to improve those figures. I see conversions from visit to opt-in of 20-50% for our highly-targeted and compelling offers. If you were to replicate the lower end of this, you would see 200 people joining your list. If your sales conversion held true, you'd be making 18 sales per month - would that prove profitable?

Content marketing is a largely iterative approach, and works best when it meets the following criteria:

1. Offers are targeted at one particular and very specific buyer persona. The prospect MUST recognise themselves in the situation you're discussing.

2. Performance and conversions are tracked, split-tested, and optimised over time. This is the only guaranteed way to improve performance over time.

3. You repeat the process. Unsurprisingly, those companies with more landing pages, offers, and email follow-up's convert exponentially more business.

My experience is limited to the world of B2B, but the above holds true for most cases I've encountered. I hope it helps.