iOS 14.5 didn't kill attribution. It killed the illusion that attribution was ever clean.
The pre-2021 model was a story. Pixel fires, attribution window matches, dashboard shows ROAS, decision flows from dashboard. The story worked because the inaccuracies cancelled out and everybody read the same flawed data, so the comparisons were valid even if the absolutes weren't.
Now the absolutes are gone too. iOS opt-in rates sit around 25 percent, view-through tracking is broken across most browsers, third-party cookies are dead in Chrome, GA4 samples aggressively, and platform self-reporting is competing with platform self-interest. The dashboards still show numbers. The numbers are mostly fiction.
The accounts winning right now stopped optimising on platform-reported ROAS as the primary signal. They moved to a three-layer stack:
Layer one. Platform-reported ROAS as a directional signal only. We still look at it. We do not bet the budget on it. If platform says ROAS is up 30 percent week over week, we treat that as a hypothesis, not a conclusion. We confirm it against layers two and three before we scale.
Layer two. First-party event taxonomy wired through Conversions API (Meta), Enhanced Conversions (Google), and equivalent on TikTok. The pixel is one input. The CRM, the cart, the call-tracking, and the closed-deal feed are the other inputs. We send the platforms the deduplicated source-of-truth events from our side, not the inferred ones from theirs. This recovers roughly 30 percent of the signal that iOS broke.
Layer three. Quarterly geo or holdout incrementality tests. The only honest measurement of paid lift. Pick a city, pause spend, watch what happens to organic + branded search + direct revenue. The delta is the true incremental contribution. Do this once a quarter for the channels that matter and you stop arguing about attribution models.
The accounts that haven't moved to this stack are doing one of two things: over-spending on retargeting because the platform attribution makes it look efficient (it isn't, the customer was going to buy anyway), or under-spending on top-of-funnel because the platform attribution undercounts the lift (it does, the customer was acquired weeks before they converted).
If your media buying team is still showing you a 7-day click ROAS as the headline metric in 2026, the team has not adapted. The numbers above the fold are the wrong numbers.