They're mostly on islands so it's very unlikely they matter at all outside of their island. If Hawaii had never been discovered, we wouldn't have to worry about losing them.

I live in a country filled with endangered "native" species but after I grew up, I learned that many of them are basically the same as common species in nearby countries, so similar that even the experts keep disagreeing on whether they're the same species or not.

If their numbers are already extremely low for a long time and everything else is doing fine, it's unlikely they're "pillars of their biome".