I believe automotive radar has a cone of sensitivity that is read as a single "pixel" worth of data. Even if the radar spun like lidar, the radar cone of sensitivity is thousands of times wider than the lidar beam so you can't make much of a picture with radar.
IIRC the data coming out of the Conti radars was preprocessed to give bearing, distance, and size of an object in the FOV of the unit. I don't know if I ever saw the true raw data out of one of them, but I'm curious what it looks like.
Ye I have a hard time imaganing how a car radar image looks like.
On boat radars it seems like the radar have really high resolution (can see much further than lidars) but have worse accuracy. I.e. things looks like blobs.
If you want more points downrange, you design your scanner to work on a smaller FOV. Some things change - you need an optical design that scans a small area in front of it somehow (faceted mirrors are popular), and at some point you need a laser source of higher quality, possibly moving away from diode lasers and towards things like fiber laser sources. This isn't conjecture BTW, this is what players like Waymo do and is evident from studying the sensor package if you're curious.
I reckon it's probably not that bad, there are big surfaces that are almost normal to what would be incoming radio energy. Stealth shapes tend to reflect energy in a completely different direction from the source.
It's cooler than that these days - under the paint are antennas plated? printed? onto the skin panels that are tuned to absorb specific frequencies of interest.
