With rootless containers, even root in the container is basically useless anyway because it truly runs as a fake ID on the host.
I’ve seen this repeated a lot, but I’m not really convinced running as root inside containers is a good/safe thing to do. User namespaces can provide some protection for the host, but that does nothing for the rest of the files inside the guest. For example, consider a server software with an arbitrary file write vulnerability. If the process is running as a low privilege user, exploiting the vulnerability might not really get you anywhere. If it’s running as root, it’s basically a free pass to root privilege and arbitrary code execution within the container.
Arch Wiki for more general info. Official docs/man pages of whatever thing you are working with for details.