“In fact, if the Meganeura, or giant dragonflies, of prehistory were still around...”
they would be physically incapable of flight under the current atmospheric conditions, so they wouldn’t be very dangerous at all, actually.
Plus the global warming and use of household chemicals would have pushed them to endangered species. And the last remaining ones would end up in the shark penis soup in China.
Actually, they’d be perfectly capable of flight, as the atmosphere wasn’t much denser back then if at all, but they would quickly suffocate, because the O2 concentration is too low to permeate their bodies properly.