You can buy much, much nicer radar than Tesla specs for their vehicles.
The stuff the DoD buys (or was buying a decade ago) is good enough to tell two basically identical tractor trailers apart based on minor features, dents/dings, etc.
Then why do automakers who support AEB not spec this radar? The Car and Driver link in my GP post above this specifically demonstrates that Tesla is not immune to failures to detect obstacles in the vehicle's path; it happens across many automakers (Subaru, Toyota, etc).
Can you share some more links to the radar technology you mention with high resolution and discrimination functionality? I am interested in performing more research on this topic. I'm familiar with several phased array radar platforms, so I might be aware of this specific implementation, but perhaps not!
As I understand it it's the algorithms that analyze the radar data that are the secret (literally) sauce. I didn't work on any of that. I just plumbed various data from A to B. I don't know much other than it was really damned good for being "legacy" at the time I was working there.
The issue isn't with the sensors, but rather the system reacting to sensor data.