Forest isn't some Boolean you can toggle 0 and 1. It's not the same forest, why would we expect the same inhabitants?
Edit: found the study https://pubmed.ncbi.nlm.nih.gov/17601136/
> Plant species richness strongly increases toward the center of the settlements, and the frequency of neutrophilous and nitrogen-demanding species is higher.
When I hear things like "delicate or unique species" I get the feeling it's not a particularly scientific conclusion.
Of course not for all insects, but I would guess that GP didn't mean highly succesful species like ants, which seem to thrive pretty much everywhere. I recommend visiting an old growth forest if you can find one in your area, they're a completely different beast compared to the ones you might be used to. It's really worth it!