This isn't a limitation of the radar sensors used, but rather in how radar works and must be implemented in a car. First, the car uses doppler radar, so it uses a difference of speed to "see" objects. Second, all still objects effectively "look" the same to the radar sensor. So, passing a road sign looks like a giant flat reflection, and the system would want to filter it out. Likewise, a stopped truck basically blends into the surroundings and gets filtered out.
Something to note is that every vehicle using radar-based EAB has the exact same problem. If someone changes lanes quickly in front of you to avoid a stationary object, you're going to hit that object.
Remember that as the photosites in a sensor get smaller and pixel density increases, electrical noise becomes a bigger and bigger problem. So doubling the resolution on a camera isn't necessarily going to give you double the usable data for the network. Further making things complex, a camera working at a high frame rate with a high resolution is going to produce an image that requires more pixels to be processed, which will require more RAM, faster busses, and bigger networks. Most existing neural nets I've seen do an unbelievable job at detecting objects and accurately classifying them on super low resolution images.
At 100 MPH, a vehicle would travel 147 feet per second. With a camera operating at 60 fps, capturing two frames for motion estimation, the object in the camera would travel around 9.7 feet. If the object is 100-200 feet away, it's not too big a deal. At 300 feet per second, that object travels 20 feet in the same 2-frame span. There aren't too many situations in which two vehicle approach one another with a speed difference of 300 feet per second, so that would be a pretty rare case. But even still, with the object covering only 20 feet of distance, the system could have worked out what it is, where it is, where it's headed, and how fast it's getting there.
At distances beyond 100-300 feet, you're probably wisest to rely on lidar or optical cameras with optics on them that are optimized for distance. This requires no increase of resolution, and would actually reduce the field of view anyway.