Basically, in games you run or play in, do creatures act according to how "they" would act and not necessarily how the DM would act?
As far as possible, I try to reflect the creatures' mental stats in the way they are portrayed. Wise creatures will use their resources well; foolish ones will not.
I mean, what tactics do a supra- genius dragon use? Certainly not any I can think of!
There's that problem, of course.
But there's also another problem with portraying the supra-genius BBEG: if you
do portray such a character with all the intelligence that by rights they should have, the game is almost certainly not going to be much fun - that supra-genius villian will identify the PCs as a
potential threat long before they become an
actual threat, and will take steps to neutralise that threat, either by recruiting them into his own service or by the application of extreme force.
The specific case of the supra-genius dragon is an interesting one, because such creatures are frequently depicted as sleeping most of the time (with Smaug being the prime example of this). That being the case, it's not unreasonable that the creature might be caught unprepared and be forced to react to an intrusion. But even then, it's near-certain that the creature would have set up several layers of early-warning mechanisms before going to sleep, allowing it to make ready before that intrusion arrives. And, faced with an unknown but hostile force, it's very likely that an early tactic is
retreat, so you can then assess the enemy forces and launch a devastating counter-attack.