There are many classic tech debates, and the question of what to formally call web addresses is one of the most nuanced. The way this normally manifests is someone asks for the “URL” to put into his or her browser, and someone perks up with, "Actually, that’s called a URI, not a URL…"
What a great title. "URLs are UI." Pithy, clear, crisp. Very true. I've been saying it for years. Someone on Twitter said "this is the professional quote of 2017" because they agreed with it. Except Jakob Nielsen said it in 1999. And Tim Berners-Lee said "Cool URIs don't change" in 1998.