Useful comparison. GenerateKeywordHistoricalMetrics is the right call once you're past a few hundred keywords. One gap worth flagging at that scale: raw search volume and competition index tell you which keywords matter, not how to group them. Once you've pulled back 5-10k keywords via the API, the next bottleneck is campaign structure: splitting by intent (brand / competitor / problem-solution / category) and match type, and deciding which keywords share a landing page. Skip that and one broad ad group ends up diluting Smart Bidding's signal no matter how good the volume data is. (Disclosure: I'm from AdeptAds, a Google Ads campaign builder; account's too new for links here, happy to share our free campaign-brief tool in a reply.)