The difference is DNS provides a fairly obvious up side

Actually, does it? Yes, the obvious upside when I type in slack.com instead of 123.45.56.67 is very good. Does this same upside apply to addresses I don't type in? What's actually the advantage of addressing one of foobarcorp's infinitude of servers uasing the string "123-45-57-78.slp05.mus.foobar.com" instead of "123.45.57.78"? It seems to just waste bytes. And most communication is of the latter sort - an app talking to its own servers managed by the same company.