In-house email will always outperform paid media, so the fact that you record a higher degree of site interaction from people who arrive via email should be of no surprise.
With regard to the advertising on Facebook and Google, what audience targeting was tested and applied? What ad formats were used? How many ad concepts were tested? What testing was done on the landing pages to improve performance? What was the "ROI" of the advertising investment, and what was the +/- on these results relative to the goals ascribed to the investment at the outset?
If you have no answers to these questions, or cannot back up your response with data from the type of testing I refer to here (which is part and parcel to running online advertising), then your article is completely pointless.
With regard to the advertising on Facebook and Google, what audience targeting was tested and applied? What ad formats were used? How many ad concepts were tested? What testing was done on the landing pages to improve performance? What was the "ROI" of the advertising investment, and what was the +/- on these results relative to the goals ascribed to the investment at the outset?
If you have no answers to these questions, or cannot back up your response with data from the type of testing I refer to here (which is part and parcel to running online advertising), then your article is completely pointless.