Actually, I managed a cat shelter with a major veterinary component, for a decade, and before that I observed feral cat colonies all over the world.  It's a universal pattern of people freaking out over cats, trying to make themselves feel better by killing a bunch of them, and then the population springs right back with a vengeance a few months later, until people try TNR and it works.  And my ecology is much deeper than yours for sure.  So, I feel confident that you are mistaken in your analysis of Hawaii's feral cat population.  I think you might be misinterpreting your anecdotal experiences.

There is no cat epedemic.  There is a humans freaking out epidemic, produced by humans failing to support and implement TNR, and major institutional players doing their darnedest to undermine it all along the way.