Let's look at this first.
An very old white dragon has a breath weapon save of Reflex DC 29. And a Frightful Presence aura of 270 ft radius with a Will DC 25. You forgot the Frightful Presence (mistake 1)
Dragon appears - party must make saves verse frightful presence. 14th level party - good saves are base +9 and poor saves are base +4. Assume a +4 for heighten stats and other misc, meaning good saves are +13 and poor saves are +8.
Cleric, Arcane Trickster, Monk need a 12 or higher to save, Ranger and Fighter need a 17 or higher to save.
Let's be generous and say the cleric, trickster and monk all save but the ranger and fighter don't save. Fighter and Ranger are now -2 to hit, saves, and skill checks due to being shaken.
Dragon breathes. Reflex save is DC 29. Reflex is poor for Cleric, Fighter, so +8 to saves for them, +13 to saves for others since they have reflex good save category.
Which means the Fighter (-2 to save for shaken) and Cleric must roll natural 20 to save, the Ranger must roll 18 or higher (-2 to save for shaken) and the others must roll 16 or higher to save.
Now....I don't know what magic items your party had, but I find it highly improbable that everyone saved verses the breath weapon and noone took any damage.
Not by RAW. Your house rule seriously slewed the outcome of this encounter (mistake 2). If the house rule applies equally, then as I showed above, about half of your party should have been stunned by the dragon's breath, since it is highly improbable that everyone saved.
By the RAW, that is not how brilliant energy weapons work (mistake 3). The dragon still has his natural armor bonuses.
There might be other factors that may be questionable.
Given the above, and your house rules and intepretation of the RAW, the outcome comes as no surprise to me. And therefore, should be no surprise to you.
If you played by the RAW, the dragon should have laid a drubbing on the party. They may have still won but it would have hard fight..... not the pathetic outcome that result.
If you posted to get a sense of what went wrong, the above shows the major problems.
If you are posting to crow about how your party took down a white dragon without any damage to themselves, then you should be aware that most people on these boards are not impressed by such bravado, particularly when it is not warranted. The dragon, by the way you played the rules, really didn't stand much of chance....