*Screams in fear*

Who could have known that a demigod as old as the world would be really powerful?

Gee, it's almost like dragons are powerful, intelligent beings who are not to be trifled with and not just something to throw in front of a party because it's in the name.

The problem is that you're combining a creature known for being solitary and long-lived with the ability to cast 9th level spells, which are especially overpowered when given prep time.
If the dragons are even the slightest bit intelligent, their lairs will be peppered with Glyphs of Warding, tons of True Polymorphed golems, and a series of Simulacrums each copied from the last (thanks to Nystul's Magic Aura letting it count as humanoid). And since the spells don't involve spell slots, those Simulacrums can cast their own 9th level spells. If you somehow do manage to kill the dragon, it will just revive from one of the many Clones in the Demiplanes it set up.
- Now I'm imagining all dragons just home-aloneing it deep inside a mountain.
- Now you're thinking like a dragon.
Yeah, metallic dragons are basically revered as minor gods in many instances. Those mfers are powerful, and they’re definitely not something that you throw at a low level party.
- All the more ridiculous that BG3 throws a silver dragon at you, almost right at the start.

27 divided by 3 = 9
Wish spell once per day with no material components cost.

That dragon's name?
Shenron
- Kharon
New NPC idea, a dragon in human form. He lives in a magical playhouse full of creatures and guests, and casts a wish every single day just doing things for fun. A nearby king must personally bring cartoons to placate the dragon.
- If you cast Wish to do stressful things there is a 1/3 chance you can't ever cast it again.
- So... Pee-wee Herman was a dragon?
- Not once per day. Wish per charisma score modifier.
  ...that dragon in human form is casting it 5x a day.
And up to 7 more 9th level spells.

If you boss dragon doesn't have time stop what is the point? Wish might be interesting but time stop in combat. Allowing it to recharge it's breath weapon and cast more spells and / or reposition. It's amazing