Yeah, it’s old news but here I go anyhow.
Had they changed the time period the movie took place in to any point before WWII then humanity getting it’s collective butt kicked by an animal vulnerable to exploding spears might have been plausible. Having them show up during a time when the military has heat-seeking missles, tanks, and undergrond fortifications designed to withstand nuclear attack is an even bigger implausibility than the existence of the dragons themselves. Every movie gets one “gimmie”, where you can bend reality around unless you’re doing fantasy. Had they made the dragons show up just after WWI when a lot of the able-bodied men were dead, cities were in ruins, weaponry had been used up, and there were no worlwide communications, then dragons hammering mankind into the ground would make sense. WWII would have been pre-empted by the dragon war and most technical advancement would have stopped. Imagine an action scene with our hero finding an old spad and going toe-to-toe with a swarm of dragons in air combat. Now that’s an action scene!