The problem with cockpit is that it lacks almost everything, while webmin has modules for almost everything. I regularly look for webmin alternatives, and though there exist a couple of nicer, cleaner ones none has more than 5% of webmin's functionality.
While there are other panels out there, Cockpit is sponsored by Red Hat. I'm not a fan of panels, but it offers more functionality out of the box than Webmin. Last time I looked there was some pretty large gaps in functionality outside of a Red Hat environment; the Ubuntu package was missing container management.
[1]: https://cockpit-project.org/