Looks like you're right:

https://www.ncbi.nlm.nih.gov/m/pubmed/22130466/

I'm guessing moderate pawpaw consumption is still relatively safe. This study isolated annnonacin from pawpaws and applied it to neural cells directly in large dosages. The soursop case involved prolonged and daily intake, as well.

The toxins are mostly in the leaves, bark, and skins, so eating them is quite safe.

Some people can have an allergic reaction when consuming them so just be aware of that when trying them for the first few times.

According to the linked article, the toxin is in the fruit pulp. I wonder if it could be bred out?

There's only a small amount in the pulp. Not an issue unless you totally gorge on them. (Similar to the Cyanide in Almonds.)

The active components have been studied for treatment of a variety of things - anti-tumor and pesticide uses being big ones:

http://www.pawpaw.kysu.edu/Pawpaw%20Acetogenins.htm

Unfortunately, it's hard to get funding to work on directly plant-derived compounds since companies can't get a monopoly on the resulting treatments.