I'm trying to understand what you mean here. The last playtest packet Black dragon seems weaker than either the Adult or Young Black Dragon. Or are you talking about the closed Alpha test instead of the the open playtest?
[table="width: 500"]
[tr]
[td][/td]
[td]Last Playtest Bestiary[/td]
[td]Young MM Dragon[/td]
[td]Adult MM Dragon[/td]
[/tr]
[tr]
[td]CR[/td]
[td]10[/td]
[td]7[/td]
[td]14[/td]
[/tr]
[tr]
[td]AC[/td]
[td]15[/td]
[td]18[/td]
[td]19[/td]
[/tr]
[tr]
[td]Bite[/td]
[td]+9 2d6+6(13)[/td]
[td]+7 2d10+4(15)[/td]
[td]+11 2d10+6(17)[/td]
[/tr]
[tr]
[td]Claw[/td]
[td]+9 1d8+6(10)[/td]
[td]+7 2d6+4(11)[/td]
[td]+11 2d6+6(15)[/td]
[/tr]
[tr]
[td]Tail[/td]
[td]+9 1d8+6(10)[/td]
[td]-[/td]
[td]+11 2d6+6(15)[/td]
[/tr]
[tr]
[td]Breath[/td]
[td]DC18 Dex 4d6+4(18)[/td]
[td]DC14 Dex 11d8(49)[/td]
[td]DC18 Dex 12d8(54)[/td]
[/tr]
[/table]
I strongly believe he meant the latest closed playtest. And I can only guess, that the claw and bite damage used to scale with size:
wyrmling, medium dragon: 1dX
young, large dragon: 2dX
adult, huge dragon, 3dX
ancient, colossal dragon 4dX
I am basing my assumption on two facts:
1. manufactured weapons seem to scale with size, gaining an additional damage die (or two in the case of a maul or great sword) per size increase.
2. The ancient green dragon´s claws seem to have their old (pre nerf) value of 4d6+STR damage.
I guess the philosophy of AC increase and damage increase by CR has changed a bit, most of the increased damage resulting from increased HP and better chance to hit. Also the number of natural weapons damage dice be determined by size seems to be only a guideline, but not a general rule: Tarrasque damage dice are all 4dX, while a hydra only has 1d10 per head.
So while raw damage per attack does not go up that much, accuracy drastically increases, even compared to their own AC they get a net increase in accuracy. (usually +2 to hit, equalling a 10% higher chance to hit itself)
If we assume a static AC of 20, your example dragons have following damage output (I use 20, because I assume a well equipped fighter should have that much AC at level 7+ and has a hard time increasing it further.
Expected damage from a young dragon bite: 0.4 * 19 = 7.6 damage on average per round from the bite.
Expected damage from an adult dragon bite: 0.6 * 21 = 12.6 damage on average per round.
Comparing that to the average HP of a level 7 fighter with 14 con: 7.6/70 = 11%
and to the average HP of a level 14 fighter: 12.6/126 7 = 10%
if you add the slightly increased damage from acid breath, and its considerably higher range and saving throw DC, and legendary actions he can take, the damage numbers seem to add up more or less correcty. (Not considering too many magic items gained on the way from level 14.)
I guess you won´t do much wrong if you increase the damage dice of adult dragons by 1 and ancient dragons by 2 if you have higher magic campaigns.
I am really looking forward to monster building guidelines.
