How to Measure the True Value of Programmatic Advertising

Hey there, I'm keen to expand my knowledge on measurement systems that can effectively show the value of programmatic advertising. Historically, last-touch attribution models from ad servers have provided these insights. However, as cookies become less reliable and clients' technical expertise increases, this 'soft-sell' approach is losing its effectiveness. There is a growing need to demonstrate programmatic's impact on business outcomes. The industry has introduced alternative measurement solutions such as viewability, time in view, and attention-based metrics. While these are useful, they can be manipulated and do not always correlate with true business value. What strategies or combinations of methods do you use to show the business impact of programmatic advertising? I'm also aware that I need to deepen my understanding of Google Analytics 4. Although GA4 offers robust post-click analysis, it might not provide comprehensive insights for a channel traditionally focused on post-view results. Thanks!