Have you seen the dragons of Dark Souls?
THEY ARE varied, powerful, and have different battle tactics... and they are rare.
Powerful?
The only one that made me nervous was the bridge red dragon,...the sewer dragon and Seath are both very easy.
Anyway, the only one that I consider a dragon is the red one...the other 2 are well....abominations
About Skyrim...I've tried Deadly Dragons and I found it...excessive...I play on Master and vanilla dragons are quite dangerous, expecially when you start to encounter Frost Dragons (and you're not a Nord...).
Elders are deadly and Ancient were nearly impossible for my character (lvl 48 assassin).
IMHO, dragons just need more damage resistance and a wider variety of shouts beside the basic breath/ball shouts...even a basic dragon should know how to use Unrelenting Force....