DNS is a horrid mess that should have been designed with ease of reading in mind. And I know that DNS was designed way before it, but I think a data transit format similar to JSON would have made the system a bit more extendable, and given people a chance to make it a more dynamic system.
E-Mail was brilliant in it's time, but for the love of all things explosive and holy is it bad. Just the fact that in it's base design there is no E2E encryption going on is a problem.
My biggest beef with the current internet is HTTP. Everything is built on it, and it isn't the greatest system. There have been so many systems and protocols implemented that did so many things, FTP/gopher/irc/etc, and most of them have gone the way of the dodo. A few hold-outs in the dedicated tech world will still use irc, but we could have done so much with cloud-based systems with FTP. And if we had a new spec for irc, would we need Slack/Discord/MS Teams/etc? They could then all talk to each other. We shouldn't be trying to reinvent the wheel, we should be using these older services in our platforms.
And don't get me thinking about cloud. The worst term that a marketing team got a hold of. At it's core, it's just somebody else's computer. And again, so much of it is build on HTTP protocols. Not many people know or remember that xWindows and X for *nix systems had a distributed system built in. Log into a server, set one environment variable to your IP address as long as you were running one of these systems yourself, and you could runs programs on the server with the GUI on your computer.