This doesn’t seem like news. The fossils of insanely big dragonflies have always indicated high levels of oxygen. You can’t have big insects without a lot of O2. Inverse law, or something.
...jumped from around 15% to around 19%. For comparison, there is 21% oxygen in today's atmosphere.
The current oxygen level is below the estimated level required to support the much larger insects in the fossil record. An amount close to 35% oxygen is required, nearly a spontaneous combustion promoting level.