A glaring omission from your original question is armor. One of the several reasons the 16HP dragon is so much more difficult than the other monsters is its whopping 5 armor. If your average Hunter or Soldier gets lucky enough to land a hit, there is a 1 in 6 chance the hit will do any damage at all (and incidentally, roughly a None in Hell chance he'll survive the following four seconds. The best defense is a massively overwhelming offense). A well coordinated group might be able to improve on this by triggering the Damage From Multiple Creatures rules (page 22) for +1 per creature after the first, but good luck keeping them that coordinated.
Yes, it's possible for a PC to have more HP than a dragon. But unless you're talking about taking a single massive hit (or some weapons with the Ignores Armor tag), the huge armor on a dragon will more than even things out.
How much damage the players take depends almost entirely on the GM's choices. When the GM gets to make a move, there are twelve default options, and only one of them is Deal Damage. That damage isn't even necessarily to a player character, and damage is often the least interesting thing that can happen. Only the last hit point really matters; any other hit point loss is just increasing the dramatic tension around the possibility of losing the last one.
Anecdotally, I once ran a two-session game in which the PCs collectively took damage a grand total of once. It was an exciting game full of action and adventure because the characters were doing exciting things, making difficult choices, and discovering interesting things about each other and the world.
General GMing advice is if you can't accept any outcome the dice may show, then don't roll the dice. You know how much HP the player has, and how much damage a hit could do. If you're not comfortable with that (and you can avoid it), simply review the list of moves and pick something else. In many cases, it can be as simple as giving the player another chance to avoid the damage by prompting them toward a defy danger move. In other cases, you can simply choose put someone in a spot instead.
This approach shouldn't play too much differently than skipping the story ahead to when the PCs had a hard fight to get where they are and everyone lost some HP. How risk-averse the group is is not up to the GM, but the GM can control how lethal he wants to be. In the end, the GM must follow the Principles and the Agenda. Filling their lives with adventure might mean trying to kill them, but it doesn't have to. If it doesn't make for a great story, then pick a different move.