Rooting your phone means you obtain root access to the device, bypassing carrier restrictions. It does not mean you run it as root user day to day. That would indeed be insecure.

Rooting is not incompatible with security. Trusting carrier distributed software on a locked down device is far less secure than using a custom install of something like Calyx or GrapheneOS.

In my view, trusting Google, Apple, Verizon, t-mobile, or at&t is incompatible with security.

The idea that people having administrative access to their own devices is inherently insecure is vicious anti-consumer nonsense.