[enriquto]

> Could someone tell me if I’ve got this right?

Yes, you got this right!

> So when the data is visualised, the perspective in the SAR image is actually 90deg

True. The extreme (and useless) case would be when the satellite is exactly in the vertical direction, then the whole image would collapse in a single point. The closer to the horizon, the best resolution you have (but then there are problems with occluding objects). As you say, there is a sort of "equivalence" between an optical image taken at an angle α from the vertical, and a radar image taken at an angle α-90.

> I get the impression that the imaging radar has no angular resolution,

True. All the antenna can do is to send a spherical wave and receive replicas of it. Conceptually, there is 0 angular resolution. In practice the beam is somewhat directed (to not waste energy), but the high resolution you see does not come from that.