I know I can't beat up Myke Tyson, despite knowing neither his or mine level.
But let's say you and three or four friends come across Mike Tyson beating up a bunch of 12-year olds? Do you say, "Well, I could never beat Mike Tyson one-on-one in a boxing ring, so we're moving on..." Or do you say, "Okay, this is going to be tough, but what can we do as a group to stack the odds in our favor so we can stop Mike Tyson from beating up on these kids?"
Seriously? PCs do not know that there are much better fighters who can fight small armies of men, wizards who can blow up buildings, clerics who can raise people from the dead? There are not stories of dragons that wipe out entire towns or even cities, regardless of armies of people fighting them?
Sorry, your premise here sounds untenable.
This is not just a random unknown monster. This is a DRAGON!!! I have never been in a D&D game ever where PCs did not automatically have knowledge that Dragons are one of the biggest, baddest monsters out there. It's never been metagaming knowledge to know that.
It's metagaming knowledge to say, "We're 1st level characters, so we don't have a chance against the dragon." A character may certainly understand that dragons are big and bad, and do everything they can to avoid having to go toe-to-toe with them. That
doesn't mean they decide to do
nothing when a town is being attacked by a dragon. They can treat the dragon like a natural disaster, and simply try to save as many regular folks as they can. They can try to find a way to drive the dragon off without engaging it directly. They can look for force equalizers.
True. But 0-level militia men are stuck with the situation that they are in. It's one thing to be stuck in a town that a dragon is attacking. It's another to walk into the situation.
In the former, there is no decision. In the latter, the decision should be based on PC motivations, not the fact that it's a game, so go for it.
Every adventure involves adventurers walking into situations that normal people avoid if they can. A dragon attacking a town is no different. How the characters respond to that is entirely up to them. Dragon over town != PCs must fight dragon to the death. They can go with no intention to fight the dragon, but just to help people. They can go because they see humanoid bad guys who are more their size. They can go because being in some kind of shelter is safer from a dragon on the wing than being out on the open road. They can go because, hey, a dragon attacking a town is a good chance to do some looting of their own! And heck, they can go just because they're adventurers and there's adventure in that thar town.
And of course, there's certainly the choice to just lie low until the whole thing blows over. The point is not that a dragon attacking a town shouldn't give the player's pause, or induce them to act carefully. The point is, a dragon attacking a town doesn't mean the only "sane" choice is to run away because the characters somehow know that they absolutely cannot defeat a dragon in a straight up fight. And here's the kicker. The game starts with the characters outside of town to give them choice in how to approach it. It would have been just as easy to start with PCs already in Greenest when the dragon and raiders attack, thereby giving them no choice in the matter.
Going to a town with a rampaging dragon flying over it sounds a bit insane.
So does the idea of going into a burning building. Nevertheless, people do it. And generally they do it in a way to mitigate the danger. And not just firefighters, either.
It's funny. In the Lost Mines of Phandelver, a boatload of people here on the boards argued that 3rd level PCs should not be stupid enough to attack a dragon, even if the module points the PCs in that direction. And if players had their PCs attack the dragon, they got what they deserved.
In this module, people here on the boards are arguing 1st level PCs should be stupid enough to go into the same town as a dragon and not only that, it's perfectly reasonable to have 2nd level PCs attack a dragon.
Which is it? Both sound dumb to me. They are DRAGONS. Duh.
In Phandelver, it's dumb to engage the dragon toe-to-toe, and the module takes pains (and encourages the DM) to discourage the players from doing that.
In this module, it's perfectly reasonable for PCs to go into a town that's being attacked by a dragon. And it's perfectly reasonable for them to attack that dragon, from the safety of the keep, along with scores of militia men. Again, the PCs are not told or expected to engage the dragon toe-to-toe. They are expected to snipe from a distance until the dragon goes away, or to find another way to drive it off (as many actual play reports have recounted).
Whatever a game designer writes into a module, even if it is contrary to the previous module, is totally good module design because it's written down?
What "contrary"? Each module has it's own context and it's own method of presenting a dragon. Each module gives the players the choice of whether to engage with the dragon. In neither module are the characters expected to kill the dragon.
But even setting that aside, there's absolutely nothing wrong with different modules presenting different playstyles. A sandbox heavy adventure might go even further than Phandelver, and have a dragon that
won't flee if reduced to half hit points, and put the choice of what to do with the dragon (fight now, fight later, avoid altogether) entirely with the players. That would be good module design for a group that wants a sandboxy module. A more linear, plot-heavy module might go even further than Hoard, and make it necessary for the players to fight the dragon, adjusting the challenge to the PCs level by either using a much weaker dragon, or by having the dragon flee after one or two hits. That would be good module design for a group that wants a plot-heavy story with balanced encounters.
As it happens, both Phandelver and Hoard take a mixed-approach, allowing for DMs to approach the adventures either way. And though that means that the DM has to make some decisions to present the module in their preferred style, that's a feature, not a bug.