One more way of measuring the effect of marketing efforts is to do a pre marketing and post marketing efforts analysis. Trending one of the key metrics like conversion rate, ROAS, click-through rate etc. If there is an upward trend, it shows that the marketing efforts have paid off however if the metric is trending downward this is not a good indicator.
Upward or downward movement is a very good indicator but other factors should be considered in making the right decision. The trending could be due to other factors like competitive effect, seasonality, etc.