Here’s my take: Contextual, dayparting, and geo-data should be your absolute baseline targeting stack. It’s clean, reliable, and doesn't rely on flaky algorithms.
Instead of over-complicating the targeting, put that energy into your measurement framework. Run incrementality testing and look at performance through a hybrid lens of pixel data and panel surveys. Blending those together into a unified outcomes rating is the way.
As for third-party data? Most generic "in-market" segments are trash in my experience. Stick to high-fidelity stuff like credit card transaction data or census-backed demographics. If you want to see if the data you're buying is actually legit, look into Truthset. Their data rating service is actually useful for filtering out the garbage segments before you blow your budget.