While you're right that they are two separate topics, they are quite closely related. Both are about the search for truth and getting a clearer picture of what

While you're right that they are two separate topics, they are quite closely related. Both are about the search for truth and getting a clearer picture of what's actually happening on your site. Looking at your 95th percentile with RUM data means something totally different than looking at your 95th percentile with synthetic data. With RUM you are looking at your actual visitors across every page on your site. With synthetic testing (Keynote, Catchpoint, etc) you're looking at a small sample of pages from random nodes in random locations around the world. The problem with synthetic testing is that it makes all sorts of assumptions about your visitors like their browser, geography, connection speed, state of browser cache, etc. This doesn't mean that synthetic testing isn't useful (it is!), but it's important to recognize the shortcomings of your methodology whether that's from looking at an average or looking only at synthetic data.