Rainbow islands is a strange port! It was released 6 years after the arcade release, and that didn't help PCE's image.
I think, same goes for Strider and Tatsujin. No matter how good these games were, this is not a wise decision!
Whereas the Snes/genesis were getting current arcade titles (when they did), we were seeing stone age arcade ports on the PCE.
I think this is one of the reasons why SNES eventually overtook the PCE.
NEC should have known better.....