That's the thing though, I do have a variety of toys. I have the Stealth Wheel and the pit with plastic bangles, Easter eggs(a foraging toy), and straws, which they love to chew and play with. I weave straws through the holes of the cage so they can take it out to get a treat. I have the barrel of monkeys they they like to take apart and throw everywhere. I have 3 foraging toy set thingies they enjoy playing on. I change their set up of toys once a month so it's new enrichment. I do the same with their fleece furnishings.
I thought it was boredom also, so I amped up all the reset type toys that they like, but they still chew heavily(less than before, but still a lot). Not to the point that they're gonna completely demolish it, though. So would it be normal that your gliders chew a lot? Obviously they do the test bites, but mine have mangled some of their plastic toys, like a swing toy they use, pretty good.
Well, if you've never been concerned with them eating anything, then I'm content with that. Whether or not they would eat the plastic and hurt or impact themselves was my main concern with them chewing so much.