Supervisor has suprevisees do peer reviews for them – what are the ethics of this?
It isn't inherently wrong to give younger members of a research group reviewing assignments (it's a legitimate and commonly used teaching tool when mentoring younger scientists), but there are two points that are definitely ethically questionable:

The review is in his name because the person quoted uploads it in his name. That's deception: The editor expects the review to be from him, in hopes of tapping his experience, but gets nothing of the sort. The younger scientist also doesn't get any credit.

There is no teaching element in all of this. Yes, there is trust, but if he never read these reviews, he can't give feedback to the younger scientist on what they could do better.


When letting younger scientists do these reviews, I often do take their (final) review after we talked about it in some detail, and prefix it by saying something along the lines

The following review was prepared by one of my graduate students. That said, we discussed it in detail, and while the words are those of the student, the conclusions are ones we share and that I believe appropriately reflect our views of the paper.

This way, the student gets to learn, and we together provide a review that meets the expectations.
In other words, I find the behavior exploitative and ethically questionable.