Demand Capture and Demand Generation Are Different Businesses
Paid search is constrained by how many people are searching. You can improve your share of that demand, but you cannot manufacture more of it, and once you own most of the high-intent query space, additional budget buys progressively worse traffic. Meta has the opposite constraint. The audience is effectively unlimited and almost entirely uninterested, so the work is convincing people who were not thinking about the problem that it is worth thinking about now.
That difference has to be reflected in how each channel is judged. A search campaign can reasonably be held to cost per qualified lead this month. A demand generation campaign shows up as branded search volume, direct traffic, faster sales conversations, higher close rates and shorter cycles, often weeks after the impression. Applying same-month last-click logic to it will always produce the same conclusion, and it will always be the wrong one.
The practical answer is to run both with different scorecards. Google Ads is measured on efficiency within existing demand. Meta is measured on blended cost of acquisition across the whole business, movement in branded search, and what people write when a form asks how they heard about you. That last field is unfashionable and remarkably informative. Between them the two scorecards describe the efficiency of the demand you captured and the volume of the demand you created.