King of the hill? Not sneak? cowardly and boring tactics? These are simply your opinion.
I cannot think of one example of a dragon in any kind of literature or pop culture that landed in front of its enemies and then took turns hitting each other. Can you give us one example that supports your take on the dragon?
Because to me it sounds like you want the dragon to be something other than what it is...which is fine, but it's a different situation than the monster's design failing to achieve what it's meant to.
Flight, speed, reach, breath weapon, legendary actions, legendary resistance, lair actions...these are all in the stat block. Having the dragon land and stand there essentially removes some of these things from the dragon's stats. Why have reach if you simply let everyone run right up to you? Why have flight if you're just going to land and go claw to axe with everyone?
It sounds like you're playing a dragon like a hill giant and then you're disappointed in the results.
Okay, mr smartypants, give us a better example of a monster that you feel is true to canon as King of the Hill.
(And don't give me simple brutes like giants)
Then, not everyone thinks the way like you do.
Have a look at
http://themonstersknow.com/dragon-tactics-part-1/
In summary, whites and red stand their ground, fighting. One supremely stupid, the other supremely arrogant. Blacks, greens and blacks, you would have much more of a point.
Then, you're misrepresenting what I'm saying. I am definitely not suggesting it shouldn't use what's in the stat block.
I am merely saying it is dead on its feet even when it does. What you're saying is that it also needs to frustrate players by flying out of visual range? That's just a crappy boring tactic. Have you seen what a level-appropriate party can do? (That is, a party perhaps five levels lower than the dragon; don't want you go hide behind "oh, the xp totals make this an easy fight, better give it some allies")
The designers sure don't seem to.
And if it was just a single (type of) monster, I would have written it off as a simple mistake.
But 5E is endemically carebearian. Almost no monsters make a challenge for properly played groups. They're laughably easy to shut down, since most of them have nothing but melee attacks (but no way to ensure the delivery of those attacks). Essentially, what you're doing is kiting them, only not simply by running around in a circle.
For single-digit CRs that might be fine, this edition being newbie friendly and all. But for CR 17? Not a chance.
So please stop denying the general - and very obvious - weakness of this edition's Monster Manual so we can get constructive!