Zen, it might not be opinion, rather species. I can assure you that the katydids I have (Microcentrum rhombifolium, Broad-winged katydid). eat leaves in my garden. They particularly loved a buddleia I had several years ago.
But with utmost respect, I question the credibility of that article you linked. The author is an "Amazon Associate ' with no listed credentials and offers no cites. The first photo captioned "Katydid eating leaf" is clearly a grasshopper. I don't question that some katydid species (there are hundreds) eat some insects, but most credible sources say they are primarily herbivorous.
Here is an excerpt from the article linked below it
"Like other Orthoptera, katydids have chewing mouthparts, and most are herbaceous but rarely cause significant plant damage to crops or ornamental plants. You may find some feeding on leaves and flowers in your garden or on your potted plants, especially in late summer. Some, especially in the tropics, are predaceous, feeding on other insects or eggs."
https://hort.extension.wisc.ed...
Also, from
http://www.biokids.umich.edu/c...
"What do they eat?
Katydids are primarily leaf-eaters. They sometimes eat other plant parts (especially flowers). They also sometimes eat dead insects, insect eggs or slow-moving insects like aphids. In the tropics some species are quite carnivorous.
I'm not trying to pick an argument here, but I've researched these insects in my garden before and knew them to chew leaves. You might have a different species.
