I finally tried switching a client's DNS to a public resolver and cut their page load complaints in half
Their office in Fresno had been blaming the ISP for slow browsing for 8 months, but swapping to Cloudflare's 1.1.1.1 knocked their average lookup time from around 90ms down to 12ms, and I'm wondering how many other "network issues" I've been troubleshooting are really just bad default DNS servers.