You're right that there's more than just last-click cost per conversion, but that doesn't mean this approach is incompatible with these extra complexities.

You might run conversion lift tests as a way to calculate the impact of increased brand awareness, and you could plug the data from these into the method outlined in the post. There you'd be looking for the optimal cost per incremental conversion rather than just optimal cost per conversion.

This is just one idea, hopefully shows that the post's method doesn't have to just use last-click conversion data.