I don't know if I've fought a cave bear but I've killed several snow bears.
My thoughts are this: Dragons could own a bear because they can fly and keep hammering fire from above. However a bear will give you all it's got on the ground and cause you much more immediate pain where a dragon circles around and gives you time to heal. So basically bears are harder briefly, even though a dragon probably takes more damage but they don't attack very fast or frequently.
Honestly I'm disappointed at dragons. They are way too easy to kill, I see one and I'm like oh cool another soul in the bag. THey should instill fear and give the player oh [censored] factor X10 over anything else. It should be an epic thing to kill one, not easier than a frost troll.