I find that not all coat hangers are the same and not all hangers are worth the money paid for them.
I use clothes pegs to keep the light weight clothes on the hanger. This clothes hanger is one of the better ones, it has a section for shoulder straps, but I still use the pegs. In this photo the top is a singlet style, so the shoulder straps fit into the cut away. The overlay (top) is a light weight fabric and used to fall off the hanger all the time.
Now the only problem I have is that most of the clothing on the dress hangers have clothes pegs on them.