I haven't used the Vengeance tech, so I can't say whether this is a bad thing or an indifferent thing. It sounds bad, especially for those who are primarily T&C Dragons, but only time will tell. Hopefully you realise the can of worms you've opened with "stronger dragons who don't need a triple-teched PV scale to be capable in combat"
Having seen certain patterns in other mmorpgs, I would say this: Nerfs (whether actual or imagined) should be balanced with "good" stuff in the same patch. In this update we Dragons have:
- Primal vengeance no longer stacks
- Drain strike costs hoard and is slower
+ Drain strike hits for more damage
+ Primal health
+ Gift of velocity
+ Extra skill points
+ New cargo disk
Whether this is balanced is up to individuals to decide. With my play style, it looks about right, maybe even a net gain.
My point is this: Please try to keep a similar per-patch balance when introducing the remaining Dragon changes (some we like, some we don't). Master this technique, and you will have bested many other mmorpg development teams.