If I understand the question correctly, you're asking how representative the data aggregated by origin is of real-user performance, as opposed to the URL-level aggregations available in PSI, Search Console, and the CrUX API. The answer is that they're both equally valid ways of aggregating user experience data, and they tell different stories about the experience.
URL-level data will help you identify whether a page has UX issues. Origin-level data will tell you whether experiences as a whole on your website are good. Some pages are more popular than others, so origin-level aggregations are an effective way of factoring in those popularity differences.
Hope that answers your question!