Not really apples to apples comparison. Their surface:volume ratio is much higher, which makes it easier to transport oxigen without any active pumping. That's why wingspan is important, since it gives a rough estimate of the volume too, knowing the bodyplan is similar to modern dragonflies. Also, their slow-paced movement requires way less oxigen than flying.

Otherwise, you could say some tapeworms can reach up to 72 ft and they only get their oxigen from passive diffusion through the skin. While true, it isn't really comparable to dragonflies.