I don't think the presence of the dragon itself is flawed design, but some of the circumstances surrounding it, such as the RP hook to slay it, really is. The druid's requirement that the PCs get the dragon to leave is also perfectly fine as an adventure goal.
The only part I have a problem with is that the adventure doesn't even hint that there may be a non-violent way to get the dragon to leave. The only option provided is to beat it down to a certain HP total. Not only is that extremely stupid for a party of that level to try it is also BORING. The dragon is a frightening combatant but it IS young and inexperienced. Clever adventurers may think of a way to get it to leave without having to fight.
Dragons like flattery, and young ones are more egotistical and likely to succumb to it than older and wiser wyrms. What if the PCs clear out Craigmaw castle and convince the dragon to move there instead? Surely a castle is more befitting a lair for so magnificent a dragon than some glorified tree house? What happens when the dragon gets older and can't fit in that puny little lair? Certainly such an awesome dragon will amass much treasure, the castle will provide ample space to store it.
Heck the PCs can tell the dragon that they cleared out the castle JUST FOR HIM!
A good adventure will provide difficult obstacles and multiple ways to overcome them. This particular challenge only offered combat as a solution. I can roll with it and offer other options as an experienced DM. The intended audience for this adventure may not know other options exist.
