The definition of ver on DLE:
- prnl. Hallarse en algún lugar, estado o situación. Verse allí. Verse pobre, abatido, agasajado.
does not help much to distinguish it "verse" from "estar" or "ser". The difference is quite small.
The way I see it, however, is that "verse" with this meaning is somewhat equivalent to the English "find oneself", i.e., it conveys a meaning of something partially unexpected and unavoidable, or at least new. This nuance is clear in your examples of "verse afectado", which are about "growing threats", "corruption scandals", and "the pandemic": all unexpected and unavoidable events.
On the other hand, "estar" is much more general and is valid in all cases. In particular, when talking about a state that has already lasted for a long time, it would be very strange to use "verse afectado", because the state is no longer new or unexpected:
Entre el 10% y el 15% de los escolares de primaria y secundaria españoles
se ven están afectados de dislexia.
in the same way as you would not say
- Between 10% and 15% of Spanish primary and secondary school students
find themselves affected by dyslexia.
Similarly, in the case of the crabs, the state is already present (because of the word "ya"), so you can say
- Si los cangrejos ya están afectados...
- Si los cangrejos ya se han visto afectados...
in past tense (actually present perfect), but you would not say
- Si los cangrejos ya
se ven afectados...