Diagnosing ROAS leaks across channels: creative vs audience vs post-click funnel

[Sophia_G]

I manage paid social ads for a mid-sized e-commerce brand, and while we're driving traffic, our overall ROAS is inconsistent and often below target, especially on newer platforms like TikTok. I suspect our issue is a combination of weak ad creative, inefficient audience targeting, and a conversion funnel that leaks after the click, but I'm struggling to isolate the biggest lever to pull first. For performance marketers, what's your systematic approach to diagnosing and improving ROAS optimization across multiple channels? How do you structure A/B tests to get clear insights on creative versus audience, and what are the key post-click metrics you analyze to understand where the funnel is breaking down before the purchase?