If Android's security model precludes owner from gaining root privileges (even over adb), then on my phone, I would prefer that model broken, thank you very much.
There are already a handful of processes running as UID 0 on Android. How, exactly, enabling "adb root" changes "threat model" or whatever lofty concepts I am supposed to care about?
I mean - assuming a competent user who is not going to install a "flashlight app with root permissions", or copy-paste things they don't understand off of internet, and such.
Your threat model must be that of Swiss cheese from air.