You either build a debug image, so you just have it, or you add your own patches adding this capability (in exactly the same way the project modifies stock aosp), and build it.
Use your own keys to sign and you're golden.
The assumption is you know what you're doing, and then it's very easy. If you don't, then you likely shouldn't.
I am not really "conflating" these in a way you suggest: it's not just about building the image but deeper understanding that will bring both.
It's not disconnected from the project, but it's inherently within the project. SURE you can consider these two separate skills, but within the context of "getting the root on the GOS build" it's one. If you don't know how to make it happen, you don't have a skill to safely use it.
And lastly, it's okay if you don't consider it a massive risk. I do.
Now let's consider the risks of that, - https://cybernews.com/security/rooted-android-ios-devices-su... - https://www.talsec.app/blog/what-is-rooting-and-how-to-prote...
For you it's not a risk, okay, I guess. I mean, if you're a security researcher with a considerable reputation, you can certainly argue with authority, but I don't see the angle.
You argue from the position of convenience and capabilities. Is the risk high? The consensus is that it is. I agree, you don't, I'm okay with it.