Oofta
Legend
When it comes to dragons - if you have a world where dragons are at least somewhat common I think it only makes sense that there will be countermeasures. It's one of the base assumptions of 5E that even dragons are not immune to mundane fighters.
Maybe the defenders have ballista on gimbals, perhaps with special chain link nets or similar. That doesn't mean the defenders don't need help with the dragons, just that in most cases dragons are not completely unstoppable without divine (or PC) intervention. Nearly all tactics of war have counters unless you're talking about world-shaking powers. In general dragons are incredibly dangerous but not unstoppable. If they were unstoppable it would be Dungeons and Dragons it would be Dragons and Slaves.
On the other hand if the normal crew is taken out, it might be a fun interlude to have to repair/man/fire the ballista to get the dragons down to where the PCs can actually fight them.
Maybe the defenders have ballista on gimbals, perhaps with special chain link nets or similar. That doesn't mean the defenders don't need help with the dragons, just that in most cases dragons are not completely unstoppable without divine (or PC) intervention. Nearly all tactics of war have counters unless you're talking about world-shaking powers. In general dragons are incredibly dangerous but not unstoppable. If they were unstoppable it would be Dungeons and Dragons it would be Dragons and Slaves.
On the other hand if the normal crew is taken out, it might be a fun interlude to have to repair/man/fire the ballista to get the dragons down to where the PCs can actually fight them.