I've been wondering, are the DLC dragons supposed to be rare encounters? I've encountered only 2 Revered Dragons (in the Forgotten Vale so they were supposed to happen), 1 Legendary Dragon (at Mount Anthor's word wall) and 1 Serpentine Dragon (at the word wall in Solstheim). Other than that, I just run into plain old Ancient Dragons. Are they supposed to be rare? I'm not complaining, Ancient Dragons are the toughest I want near my house.

I'm not sure.

Like you, I've only had 4 Revered; 2 at the Forgotten Vale, 2 random attacks.
Only 1 Legendary Dragon.

Unless you're a maxed level, you should get them more. I primarily run into legendary and ancient dragons. I'm also 81.